diff --git a/lib/editor/atto/yui/build/moodle-editor_atto-editor/moodle-editor_atto-editor-debug.js b/lib/editor/atto/yui/build/moodle-editor_atto-editor/moodle-editor_atto-editor-debug.js
index a3e1b563395..98084c9280b 100644
--- a/lib/editor/atto/yui/build/moodle-editor_atto-editor/moodle-editor_atto-editor-debug.js
+++ b/lib/editor/atto/yui/build/moodle-editor_atto-editor/moodle-editor_atto-editor-debug.js
@@ -740,38 +740,50 @@ EditorToolbarNav.prototype = {
         // Prevent the default browser behaviour.
         e.preventDefault();
 
-        var buttons = this.toolbar.all('button');
-
         // On cursor moves we loops through the buttons.
-        var found = false,
-            index = 0,
+        var buttons = this.toolbar.all('button'),
             direction = 1,
-            checkCount = 0,
-            group,
-            candidate,
             button,
             current = e.target.ancestor('button', true);
 
-        // Determine which button is currently selected.
-        while (!found && index < buttons.size()) {
-            if (buttons.item(index) === current) {
-                found = true;
-            } else {
-                index++;
-            }
-        }
-
-        if (!found) {
-            Y.log("Unable to find this button in the list of buttons", 'debug', LOGNAME);
-            return;
-        }
-
         if (e.keyCode === 37) {
             // Moving left so reverse the direction.
             direction = -1;
         }
 
-        // Try to find the next
+        button = this._findFirstFocusable(buttons, current, direction);
+        if (button) {
+            button.focus();
+        } else {
+            Y.log("Unable to find a button to focus on", 'debug', LOGNAME);
+        }
+    },
+
+    /**
+     * Find the first focusable button.
+     *
+     * @param {NodeList} buttons A list of nodes.
+     * @param {Node} startAt The node in the list to start the search from.
+     * @param {Number} direction The direction in which to search (1 or -1).
+     * @return {Node | Undefined} The Node or undefined.
+     * @method _findFirstFocusable
+     * @private
+     */
+    _findFirstFocusable: function(buttons, startAt, direction) {
+        var checkCount = 0,
+            group,
+            candidate,
+            button,
+            index;
+
+        // Determine which button to start the search from.
+        index = buttons.indexOf(startAt);
+        if (index < -1) {
+            Y.log("Unable to find the button in the list of buttons", 'debug', LOGNAME);
+            index = 0;
+        }
+
+        // Try to find the next.
         while (checkCount < buttons.size()) {
             index += direction;
             if (index < 0) {
@@ -802,12 +814,35 @@ EditorToolbarNav.prototype = {
             break;
         }
 
-        if (button) {
-            button.focus();
-            this._setTabFocus(button);
-        } else {
-            Y.log("Unable to find a button to focus on", 'debug', LOGNAME);
+        return button;
+    },
+
+    /**
+     * Check the tab focus.
+     *
+     * When we disable or hide a button, we should call this method to ensure that the
+     * focus is not currently set on an inaccessible button, otherwise tabbing to the toolbar
+     * would be impossible.
+     *
+     * @method checkTabFocus
+     * @chainable
+     */
+    checkTabFocus: function() {
+        if (this._tabFocus) {
+            if (this._tabFocus.hasAttribute('disabled') || this._tabFocus.hasAttribute('hidden')
+                    || this._tabFocus.ancestor('.atto_group').hasAttribute('hidden')) {
+                // Find first available button.
+                button = this._findFirstFocusable(this.toolbar.all('button'), this._tabFocus, -1);
+                if (button) {
+                    if (this._tabFocus.compareTo(document.activeElement)) {
+                        // We should also move the focus, because the inaccessible button also has the focus.
+                        button.focus();
+                    }
+                    this._setTabFocus(button);
+                }
+            }
         }
+        return this;
     },
 
     /**
diff --git a/lib/editor/atto/yui/build/moodle-editor_atto-editor/moodle-editor_atto-editor-min.js b/lib/editor/atto/yui/build/moodle-editor_atto-editor/moodle-editor_atto-editor-min.js
index c0ac46f7273..c2cf00d1fe7 100644
--- a/lib/editor/atto/yui/build/moodle-editor_atto-editor/moodle-editor_atto-editor-min.js
+++ b/lib/editor/atto/yui/build/moodle-editor_atto-editor/moodle-editor_atto-editor-min.js
@@ -1,2 +1,2 @@
-YUI.add("moodle-editor_atto-editor",function(e,t){function i(){i.superclass.constructor.apply(this,arguments)}function s(){}function o(){}function u(){}function a(){}function f(){}function l(){}function c(){}var n="moodle-editor_atto-editor",r={CONTENT:"editor_atto_content",CONTENTWRAPPER:"editor_atto_content_wrap",TOOLBAR:"editor_atto_toolbar",WRAPPER:"editor_atto",HIGHLIGHT:"highlight"};e.extend(i,e.Base,{BLOCK_TAGS:["address","article","aside","audio","blockquote","canvas","dd","div","dl","fieldset","figcaption","figure","footer","form","h1","h2","h3","h4","h5","h6","header","hgroup","hr","noscript","ol","output","p","pre","section","table","tfoot","ul","video"],PLACEHOLDER_FONTNAME:"yui-tmp",ALL_NODES_SELECTOR:"[style],font[face]",FONT_FAMILY:"fontFamily",_wrapper:null,editor:null,textarea:null,textareaLabel:null,plugins:null,initializer:function(){var t;this.textarea=e.one(document.getElementById(this.get("elementid")));if(!this.textarea)return;this._wrapper=e.Node.create('<div class="'+r.WRAPPER+'" />'),t=e.Handlebars.compile('<div id="{{elementid}}editable" contenteditable="true" role="textbox" spellcheck="true" aria-live="off" class="{{CSS.CONTENT}}" />'),this.editor=e.Node.create(t({elementid:this.get("elementid"),CSS:r})),this.textareaLabel=e.one('[for="'+this.get("elementid")+'"]'),this.textareaLabel&&(this.textareaLabel.generateID(),this.editor.setAttribute("aria-labelledby",this.textareaLabel.get("id"))),this.setupToolbar();var n=e.Node.create('<div class="'+r.CONTENTWRAPPER+'" />');n.appendChild(this.editor),this._wrapper.appendChild(n),this.editor.setStyle("minHeight",1.2*this.textarea.getAttribute("rows")+"em"),this.disableCssStyling(),this.textarea.get("parentNode").insert(this._wrapper,this.textarea),this.textarea.hide(),this.updateFromTextArea(),this.publishEvents(),this.setupSelectionWatchers(),this.setupPlugins()},focus:function(){return this.editor.focus(),this},publishEvents:function(){return this.publish("change",{broadcast:!0,preventable:!0}),this.publish("pluginsloaded",{fireOnce:!0}),this.publish("atto:selectionchanged",{prefix:"atto"}),e.delegate(["mouseup","keyup","focus"],this._hasSelectionChanged,document.body,"."+r.CONTENT,this),this},setupPlugins:function(){this.plugins={};var t=this.get("plugins"),n,r,i,s,o;for(n in t){r=t[n];if(!r.plugins)continue;for(i in r.plugins){s=r.plugins[i],o=e.mix({name:s.name,group:r.group,editor:this.editor,toolbar:this.toolbar,host:this},s);if(typeof e.M["atto_"+s.name]=="undefined")continue;this.plugins[s.name]=new e.M["atto_"+s.name].Button(o)}}return this.fire("pluginsloaded"),this},enablePlugins:function(e){this._setPluginState(!0,e)},disablePlugins:function(e){this._setPluginState(!1,e)},_setPluginState:function(t,n){var r="disableButtons";t&&(r="enableButtons"),n?this.plugins[n][r]():e.Object.each(this.plugins,function(e){e[r]()},this)}},{NS:"editor_atto",ATTRS:{elementid:{value:null,writeOnce:!0},plugins:{value:{},writeOnce:!0}}}),e.augment(i,e.EventTarget),e.namespace("M.editor_atto").Editor=i,e.namespace("M.editor_atto.Editor").init=function(t){return new e.M.editor_atto.Editor(t)},s.ATTRS={},s.prototype={updateFromTextArea:function(){this.editor.setHTML(""),this.editor.append(this.textarea.get("value")),this.cleanEditorHTML(),this.editor.getHTML()===""&&(e.UA.ie&&e.UA.ie<10?this.editor.setHTML("<p></p>"):this.editor.setHTML("<p><br></p>"))},updateOriginal:function(){this.textarea.set("value",this.getCleanHTML()),this.textarea.simulate("change"),this.fire("change")}},e.Base.mix(e.M.editor_atto.Editor,[s]),o.ATTRS={},o.prototype={getCleanHTML:function(){var t=this.editor.cloneNode(!0);return e.each(t.all('[id^="yui"]'),function(e){e.removeAttribute("id")}),t.all(".atto_control").remove(!0),this._cleanHTML(t.get("innerHTML"))},cleanEditorHTML:function(){var e=this.editor.get("innerHTML");return this.editor.set("innerHTML",this._cleanHTML(e)),this},_cleanHTML:function(e){var t=[{regex:/<!--[\s\S]*?-->/gi,replace:""},{regex:/<\\?\?xml[^>]*>/gi,replace:""},{regex:/<\/?\w+:[^>]*>/gi,replace:""},{regex:/\s*MSO[-:][^;"']*;?/gi,replace:""},{regex:/<span[^>]*>(&nbsp;|\s)*<\/span>/gi,replace:""},{regex:/class="Mso[^"]*"/gi,replace:""},{regex:/<(\/?title|\/?meta|\/?style|\/?st\d|\/?head|\/?font|\/?html|\/?body|!\[)[^>]*?>/gi,replace:""},{regex:new RegExp(String.fromCharCode(8220),"gi"),replace:'"'},{regex:new RegExp(String.fromCharCode(8216),"gi"),replace:"'"},{regex:new RegExp(String.fromCharCode(8217),"gi"),replace:"'"},{regex:new RegExp(String.fromCharCode(8211),"gi"),replace:"-"},{regex:new RegExp(String.fromCharCode(8212),"gi"),replace:"--"},{regex:new RegExp(String.fromCharCode(189),"gi"),replace:"1/2"},{regex:new RegExp(String.fromCharCode(188),"gi"),replace:"1/4"},{regex:new RegExp(String.fromCharCode(190),"gi"),replace:"3/4"},{regex:new RegExp(String.fromCharCode(169),"gi"),replace:"(c)"},{regex:new RegExp(String.fromCharCode(174),"gi"),replace:"(r)"},{regex:new RegExp(String.fromCharCode(8230),"gi"),replace:"..."}],n=0;for(n=0;n<t.length;n++)e=e.replace(t[n].regex,t[n].replace);return e}},e.Base.mix(e.M.editor_atto.Editor,[o]),u.ATTRS={},u.prototype={toolbar:null,setupToolbar:function(){return this.toolbar=e.Node.create('<div class="'+r.TOOLBAR+'" role="toolbar" aria-live="off"/>'),this._wrapper.appendChild(this.toolbar),this.textareaLabel&&this.toolbar.setAttribute("aria-labelledby",this.textareaLabel.get("id")),this.setupToolbarNavigation(),this}},e.Base.mix(e.M.editor_atto.Editor,[u]),a.ATTRS={},a.prototype={_tabFocus:null,setupToolbarNavigation:function(){return this._wrapper.delegate("key",this.toolbarKeyboardNavigation,"down:37,39","."+r.TOOLBAR,this),this},toolbarKeyboardNavigation:function(e){e.preventDefault();var t=this.toolbar.all("button"),n=!1,r=0,i=1,s=0,o,u,a,f=e.target.ancestor("button",!0);while(!n&&r<t.size())t.item(r)===f?n=!0:r++;if(!n)return;e.keyCode===37&&(i=-1);while(s<t.size()){r+=i,r<0?r=t.size()-1:r>=t.size()&&(r=0),u=t.item(r),s++;if(u.hasAttribute("hidden")||u.hasAttribute("disabled"))continue;
-o=u.ancestor(".atto_group");if(o.hasAttribute("hidden"))continue;a=u;break}a&&(a.focus(),this._setTabFocus(a))},_setTabFocus:function(e){return this._tabFocus&&this._tabFocus.setAttribute("tabindex","-1"),this._tabFocus=e,this._tabFocus.setAttribute("tabindex",0),this.toolbar.setAttribute("aria-activedescendant",this._tabFocus.generateID()),this}},e.Base.mix(e.M.editor_atto.Editor,[a]),f.ATTRS={},f.prototype={_selections:null,_lastSelection:null,_focusFromClick:!1,setupSelectionWatchers:function(){return this.on("atto:selectionchanged",this.saveSelection,this),this.editor.on("focus",this.restoreSelection,this),this.editor.on("mousedown",function(){this._focusFromClick=!0},this),this.editor.on("blur",function(){this._focusFromClick=!1,this.updateOriginal()},this),this},isActive:function(){var e=rangy.createRange(),t=rangy.getSelection();return t.rangeCount?(e.selectNode(this.editor.getDOMNode()),e.intersectsRange(t.getRangeAt(0))):!1},getSelectionFromNode:function(e){var t=rangy.createRange();return t.selectNode(e.getDOMNode()),[t]},saveSelection:function(){this.isActive()&&(this._selections=this.getSelection())},restoreSelection:function(){this._focusFromClick||this._selections&&this.setSelection(this._selections),this._focusFromClick=!1},getSelection:function(){return rangy.getSelection().getAllRanges()},selectionContainsNode:function(e){return rangy.getSelection().containsNode(e.getDOMNode(),!0)},selectionFilterMatches:function(e,t,n){typeof n=="undefined"&&(n=!0),t||(t=this.getSelectedNodes());var r=t.size()>0,i=!1,s=this.editor,o=function(e){s.contains(e)};return t.each(function(t){if(n){if(!r||!t.ancestor(e,!0,o))r=!1}else!i&&t.ancestor(e,!0,o)&&(i=!0)},this),n?r:i},getSelectedNodes:function(){var t=new e.NodeList,n,r,i,s,o;r=rangy.getSelection(),r.rangeCount?i=r.getRangeAt(0):i=rangy.createRange(),i.collapsed&&(i=i.cloneRange(),i.selectNode(i.commonAncestorContainer)),n=i.getNodes();for(o=0;o<n.length;o++)s=e.one(n[o]),this.editor.contains(s)&&t.push(s);return t},_hasSelectionChanged:function(e){var t=rangy.getSelection(),n,r=!1;return t.rangeCount?n=t.getRangeAt(0):n=rangy.createRange(),this._lastSelection&&!this._lastSelection.equals(n)?(r=!0,this._fireSelectionChanged(e)):(this._lastSelection=n,r)},_fireSelectionChanged:function(e){this.fire("atto:selectionchanged",{event:e,selectedNodes:this.getSelectedNodes()})},getSelectionParentNode:function(){var e=rangy.getSelection();return e.rangeCount?e.getRangeAt(0).commonAncestorContainer:!1},setSelection:function(e){var t=rangy.getSelection();t.setRanges(e)},formatSelectionBlock:function(t,n){var r=this.getSelectionParentNode(),i,s,o,u,a,f;if(!r)return!1;i=this.editor,r=e.one(r),s=r.ancestor(function(e){var t=e.get("tagName");return t&&(t=t.toLowerCase()),e===i||t==="td"||t==="th"},!0),s&&(i=s),o=r.ancestor(this.BLOCK_TAGS.join(", "),!0),o&&(a=o.ancestor(function(e){return e===i},!1),a||(o=!1)),o||(u=e.Node.create("<p></p>"),i.get("childNodes").each(function(e){u.append(e.remove())}),i.append(u),o=u),t&&t!==""&&(f=e.Node.create("<"+t+"></"+t+">"),f.setAttrs(o.getAttrs()),o.get("childNodes").each(function(e){e.remove(),f.append(e)}),o.replace(f),o=f),n&&o.setAttrs(n);var l=this.getSelectionFromNode(o);return this.setSelection(l),o},insertContentAtFocusPoint:function(t){var n=rangy.getSelection(),r,i=e.Node.create(t);n.rangeCount&&(r=n.getRangeAt(0)),r&&(r.deleteContents(),r.insertNode(i.getDOMNode()))}},e.Base.mix(e.M.editor_atto.Editor,[f]),l.ATTRS={},l.prototype={disableCssStyling:function(){try{document.execCommand("styleWithCSS",0,!1)}catch(e){try{document.execCommand("useCSS",0,!0)}catch(t){try{document.execCommand("styleWithCSS",!1,!1)}catch(n){}}}},enableCssStyling:function(){try{document.execCommand("styleWithCSS",0,!0)}catch(e){try{document.execCommand("useCSS",0,!1)}catch(t){try{document.execCommand("styleWithCSS",!1,!0)}catch(n){}}}},toggleInlineSelectionClass:function(t){var n=this.getSelectionParentNode(),r,i=[],s,o,u,a=0;if(!n)return;document.execCommand("fontname",!1,this.PLACEHOLDER_FONTNAME),r=this.editor.all(this.ALL_NODES_SELECTOR),r.each(function(t,n){t.getStyle(this.FONT_FAMILY)===this.PLACEHOLDER_FONTNAME&&(t.setStyle(this.FONT_FAMILY,""),t.compareTo(this.editor)||i.push(e.Node.getDOMNode(r.item(n))))});for(a=0;a<i.length;a++){o=e.one(i[a]),s=o.ancestor(".editor_atto_content span"),s?o=s:(u=e.Node.create("<span></span>"),u.append(i[a].innerHTML),o.replace(u),o=u);for(var f=0;f<t.length;f++)o.toggleClass(t[f])}}},e.Base.mix(e.M.editor_atto.Editor,[l]),c.ATTRS={filepickeroptions:{value:{}}},c.prototype={canShowFilepicker:function(e){return typeof this.get("filepickeroptions")[e]!="undefined"},showFilepicker:function(t,n,r){var i=this;e.use("core_filepicker",function(e){var s=e.clone(i.get("filepickeroptions")[t],!0);s.formcallback=n,r&&(s.magicscope=r),M.core_filepicker.show(e,s)})}},e.Base.mix(e.M.editor_atto.Editor,[c])},"@VERSION@",{requires:["node","io","overlay","escape","event","event-simulate","event-custom","yui-throttle","moodle-core-notification-dialogue","moodle-editor_atto-rangy","handlebars"]});
+YUI.add("moodle-editor_atto-editor",function(e,t){function i(){i.superclass.constructor.apply(this,arguments)}function s(){}function o(){}function u(){}function a(){}function f(){}function l(){}function c(){}var n="moodle-editor_atto-editor",r={CONTENT:"editor_atto_content",CONTENTWRAPPER:"editor_atto_content_wrap",TOOLBAR:"editor_atto_toolbar",WRAPPER:"editor_atto",HIGHLIGHT:"highlight"};e.extend(i,e.Base,{BLOCK_TAGS:["address","article","aside","audio","blockquote","canvas","dd","div","dl","fieldset","figcaption","figure","footer","form","h1","h2","h3","h4","h5","h6","header","hgroup","hr","noscript","ol","output","p","pre","section","table","tfoot","ul","video"],PLACEHOLDER_FONTNAME:"yui-tmp",ALL_NODES_SELECTOR:"[style],font[face]",FONT_FAMILY:"fontFamily",_wrapper:null,editor:null,textarea:null,textareaLabel:null,plugins:null,initializer:function(){var t;this.textarea=e.one(document.getElementById(this.get("elementid")));if(!this.textarea)return;this._wrapper=e.Node.create('<div class="'+r.WRAPPER+'" />'),t=e.Handlebars.compile('<div id="{{elementid}}editable" contenteditable="true" role="textbox" spellcheck="true" aria-live="off" class="{{CSS.CONTENT}}" />'),this.editor=e.Node.create(t({elementid:this.get("elementid"),CSS:r})),this.textareaLabel=e.one('[for="'+this.get("elementid")+'"]'),this.textareaLabel&&(this.textareaLabel.generateID(),this.editor.setAttribute("aria-labelledby",this.textareaLabel.get("id"))),this.setupToolbar();var n=e.Node.create('<div class="'+r.CONTENTWRAPPER+'" />');n.appendChild(this.editor),this._wrapper.appendChild(n),this.editor.setStyle("minHeight",1.2*this.textarea.getAttribute("rows")+"em"),this.disableCssStyling(),this.textarea.get("parentNode").insert(this._wrapper,this.textarea),this.textarea.hide(),this.updateFromTextArea(),this.publishEvents(),this.setupSelectionWatchers(),this.setupPlugins()},focus:function(){return this.editor.focus(),this},publishEvents:function(){return this.publish("change",{broadcast:!0,preventable:!0}),this.publish("pluginsloaded",{fireOnce:!0}),this.publish("atto:selectionchanged",{prefix:"atto"}),e.delegate(["mouseup","keyup","focus"],this._hasSelectionChanged,document.body,"."+r.CONTENT,this),this},setupPlugins:function(){this.plugins={};var t=this.get("plugins"),n,r,i,s,o;for(n in t){r=t[n];if(!r.plugins)continue;for(i in r.plugins){s=r.plugins[i],o=e.mix({name:s.name,group:r.group,editor:this.editor,toolbar:this.toolbar,host:this},s);if(typeof e.M["atto_"+s.name]=="undefined")continue;this.plugins[s.name]=new e.M["atto_"+s.name].Button(o)}}return this.fire("pluginsloaded"),this},enablePlugins:function(e){this._setPluginState(!0,e)},disablePlugins:function(e){this._setPluginState(!1,e)},_setPluginState:function(t,n){var r="disableButtons";t&&(r="enableButtons"),n?this.plugins[n][r]():e.Object.each(this.plugins,function(e){e[r]()},this)}},{NS:"editor_atto",ATTRS:{elementid:{value:null,writeOnce:!0},plugins:{value:{},writeOnce:!0}}}),e.augment(i,e.EventTarget),e.namespace("M.editor_atto").Editor=i,e.namespace("M.editor_atto.Editor").init=function(t){return new e.M.editor_atto.Editor(t)},s.ATTRS={},s.prototype={updateFromTextArea:function(){this.editor.setHTML(""),this.editor.append(this.textarea.get("value")),this.cleanEditorHTML(),this.editor.getHTML()===""&&(e.UA.ie&&e.UA.ie<10?this.editor.setHTML("<p></p>"):this.editor.setHTML("<p><br></p>"))},updateOriginal:function(){this.textarea.set("value",this.getCleanHTML()),this.textarea.simulate("change"),this.fire("change")}},e.Base.mix(e.M.editor_atto.Editor,[s]),o.ATTRS={},o.prototype={getCleanHTML:function(){var t=this.editor.cloneNode(!0);return e.each(t.all('[id^="yui"]'),function(e){e.removeAttribute("id")}),t.all(".atto_control").remove(!0),this._cleanHTML(t.get("innerHTML"))},cleanEditorHTML:function(){var e=this.editor.get("innerHTML");return this.editor.set("innerHTML",this._cleanHTML(e)),this},_cleanHTML:function(e){var t=[{regex:/<!--[\s\S]*?-->/gi,replace:""},{regex:/<\\?\?xml[^>]*>/gi,replace:""},{regex:/<\/?\w+:[^>]*>/gi,replace:""},{regex:/\s*MSO[-:][^;"']*;?/gi,replace:""},{regex:/<span[^>]*>(&nbsp;|\s)*<\/span>/gi,replace:""},{regex:/class="Mso[^"]*"/gi,replace:""},{regex:/<(\/?title|\/?meta|\/?style|\/?st\d|\/?head|\/?font|\/?html|\/?body|!\[)[^>]*?>/gi,replace:""},{regex:new RegExp(String.fromCharCode(8220),"gi"),replace:'"'},{regex:new RegExp(String.fromCharCode(8216),"gi"),replace:"'"},{regex:new RegExp(String.fromCharCode(8217),"gi"),replace:"'"},{regex:new RegExp(String.fromCharCode(8211),"gi"),replace:"-"},{regex:new RegExp(String.fromCharCode(8212),"gi"),replace:"--"},{regex:new RegExp(String.fromCharCode(189),"gi"),replace:"1/2"},{regex:new RegExp(String.fromCharCode(188),"gi"),replace:"1/4"},{regex:new RegExp(String.fromCharCode(190),"gi"),replace:"3/4"},{regex:new RegExp(String.fromCharCode(169),"gi"),replace:"(c)"},{regex:new RegExp(String.fromCharCode(174),"gi"),replace:"(r)"},{regex:new RegExp(String.fromCharCode(8230),"gi"),replace:"..."}],n=0;for(n=0;n<t.length;n++)e=e.replace(t[n].regex,t[n].replace);return e}},e.Base.mix(e.M.editor_atto.Editor,[o]),u.ATTRS={},u.prototype={toolbar:null,setupToolbar:function(){return this.toolbar=e.Node.create('<div class="'+r.TOOLBAR+'" role="toolbar" aria-live="off"/>'),this._wrapper.appendChild(this.toolbar),this.textareaLabel&&this.toolbar.setAttribute("aria-labelledby",this.textareaLabel.get("id")),this.setupToolbarNavigation(),this}},e.Base.mix(e.M.editor_atto.Editor,[u]),a.ATTRS={},a.prototype={_tabFocus:null,setupToolbarNavigation:function(){return this._wrapper.delegate("key",this.toolbarKeyboardNavigation,"down:37,39","."+r.TOOLBAR,this),this},toolbarKeyboardNavigation:function(e){e.preventDefault();var t=this.toolbar.all("button"),n=1,r,i=e.target.ancestor("button",!0);e.keyCode===37&&(n=-1),r=this._findFirstFocusable(t,i,n),r&&r.focus()},_findFirstFocusable:function(e,t,n){var r=0,i,s,o,u;u=e.indexOf(t),u<-1&&(u=0);while(r<e.size()){u+=n,u<0?u=e.size()-1:u>=e.size()&&(u=0),s=e.item(u),r++;if(s.hasAttribute
+("hidden")||s.hasAttribute("disabled"))continue;i=s.ancestor(".atto_group");if(i.hasAttribute("hidden"))continue;o=s;break}return o},checkTabFocus:function(){return this._tabFocus&&(this._tabFocus.hasAttribute("disabled")||this._tabFocus.hasAttribute("hidden")||this._tabFocus.ancestor(".atto_group").hasAttribute("hidden"))&&(button=this._findFirstFocusable(this.toolbar.all("button"),this._tabFocus,-1),button&&(this._tabFocus.compareTo(document.activeElement)&&button.focus(),this._setTabFocus(button))),this},_setTabFocus:function(e){return this._tabFocus&&this._tabFocus.setAttribute("tabindex","-1"),this._tabFocus=e,this._tabFocus.setAttribute("tabindex",0),this.toolbar.setAttribute("aria-activedescendant",this._tabFocus.generateID()),this}},e.Base.mix(e.M.editor_atto.Editor,[a]),f.ATTRS={},f.prototype={_selections:null,_lastSelection:null,_focusFromClick:!1,setupSelectionWatchers:function(){return this.on("atto:selectionchanged",this.saveSelection,this),this.editor.on("focus",this.restoreSelection,this),this.editor.on("mousedown",function(){this._focusFromClick=!0},this),this.editor.on("blur",function(){this._focusFromClick=!1,this.updateOriginal()},this),this},isActive:function(){var e=rangy.createRange(),t=rangy.getSelection();return t.rangeCount?(e.selectNode(this.editor.getDOMNode()),e.intersectsRange(t.getRangeAt(0))):!1},getSelectionFromNode:function(e){var t=rangy.createRange();return t.selectNode(e.getDOMNode()),[t]},saveSelection:function(){this.isActive()&&(this._selections=this.getSelection())},restoreSelection:function(){this._focusFromClick||this._selections&&this.setSelection(this._selections),this._focusFromClick=!1},getSelection:function(){return rangy.getSelection().getAllRanges()},selectionContainsNode:function(e){return rangy.getSelection().containsNode(e.getDOMNode(),!0)},selectionFilterMatches:function(e,t,n){typeof n=="undefined"&&(n=!0),t||(t=this.getSelectedNodes());var r=t.size()>0,i=!1,s=this.editor,o=function(e){s.contains(e)};return t.each(function(t){if(n){if(!r||!t.ancestor(e,!0,o))r=!1}else!i&&t.ancestor(e,!0,o)&&(i=!0)},this),n?r:i},getSelectedNodes:function(){var t=new e.NodeList,n,r,i,s,o;r=rangy.getSelection(),r.rangeCount?i=r.getRangeAt(0):i=rangy.createRange(),i.collapsed&&(i=i.cloneRange(),i.selectNode(i.commonAncestorContainer)),n=i.getNodes();for(o=0;o<n.length;o++)s=e.one(n[o]),this.editor.contains(s)&&t.push(s);return t},_hasSelectionChanged:function(e){var t=rangy.getSelection(),n,r=!1;return t.rangeCount?n=t.getRangeAt(0):n=rangy.createRange(),this._lastSelection&&!this._lastSelection.equals(n)?(r=!0,this._fireSelectionChanged(e)):(this._lastSelection=n,r)},_fireSelectionChanged:function(e){this.fire("atto:selectionchanged",{event:e,selectedNodes:this.getSelectedNodes()})},getSelectionParentNode:function(){var e=rangy.getSelection();return e.rangeCount?e.getRangeAt(0).commonAncestorContainer:!1},setSelection:function(e){var t=rangy.getSelection();t.setRanges(e)},formatSelectionBlock:function(t,n){var r=this.getSelectionParentNode(),i,s,o,u,a,f;if(!r)return!1;i=this.editor,r=e.one(r),s=r.ancestor(function(e){var t=e.get("tagName");return t&&(t=t.toLowerCase()),e===i||t==="td"||t==="th"},!0),s&&(i=s),o=r.ancestor(this.BLOCK_TAGS.join(", "),!0),o&&(a=o.ancestor(function(e){return e===i},!1),a||(o=!1)),o||(u=e.Node.create("<p></p>"),i.get("childNodes").each(function(e){u.append(e.remove())}),i.append(u),o=u),t&&t!==""&&(f=e.Node.create("<"+t+"></"+t+">"),f.setAttrs(o.getAttrs()),o.get("childNodes").each(function(e){e.remove(),f.append(e)}),o.replace(f),o=f),n&&o.setAttrs(n);var l=this.getSelectionFromNode(o);return this.setSelection(l),o},insertContentAtFocusPoint:function(t){var n=rangy.getSelection(),r,i=e.Node.create(t);n.rangeCount&&(r=n.getRangeAt(0)),r&&(r.deleteContents(),r.insertNode(i.getDOMNode()))}},e.Base.mix(e.M.editor_atto.Editor,[f]),l.ATTRS={},l.prototype={disableCssStyling:function(){try{document.execCommand("styleWithCSS",0,!1)}catch(e){try{document.execCommand("useCSS",0,!0)}catch(t){try{document.execCommand("styleWithCSS",!1,!1)}catch(n){}}}},enableCssStyling:function(){try{document.execCommand("styleWithCSS",0,!0)}catch(e){try{document.execCommand("useCSS",0,!1)}catch(t){try{document.execCommand("styleWithCSS",!1,!0)}catch(n){}}}},toggleInlineSelectionClass:function(t){var n=this.getSelectionParentNode(),r,i=[],s,o,u,a=0;if(!n)return;document.execCommand("fontname",!1,this.PLACEHOLDER_FONTNAME),r=this.editor.all(this.ALL_NODES_SELECTOR),r.each(function(t,n){t.getStyle(this.FONT_FAMILY)===this.PLACEHOLDER_FONTNAME&&(t.setStyle(this.FONT_FAMILY,""),t.compareTo(this.editor)||i.push(e.Node.getDOMNode(r.item(n))))});for(a=0;a<i.length;a++){o=e.one(i[a]),s=o.ancestor(".editor_atto_content span"),s?o=s:(u=e.Node.create("<span></span>"),u.append(i[a].innerHTML),o.replace(u),o=u);for(var f=0;f<t.length;f++)o.toggleClass(t[f])}}},e.Base.mix(e.M.editor_atto.Editor,[l]),c.ATTRS={filepickeroptions:{value:{}}},c.prototype={canShowFilepicker:function(e){return typeof this.get("filepickeroptions")[e]!="undefined"},showFilepicker:function(t,n,r){var i=this;e.use("core_filepicker",function(e){var s=e.clone(i.get("filepickeroptions")[t],!0);s.formcallback=n,r&&(s.magicscope=r),M.core_filepicker.show(e,s)})}},e.Base.mix(e.M.editor_atto.Editor,[c])},"@VERSION@",{requires:["node","io","overlay","escape","event","event-simulate","event-custom","yui-throttle","moodle-core-notification-dialogue","moodle-editor_atto-rangy","handlebars"]});
diff --git a/lib/editor/atto/yui/build/moodle-editor_atto-editor/moodle-editor_atto-editor.js b/lib/editor/atto/yui/build/moodle-editor_atto-editor/moodle-editor_atto-editor.js
index 43ea641ff26..c03a1c38bfb 100644
--- a/lib/editor/atto/yui/build/moodle-editor_atto-editor/moodle-editor_atto-editor.js
+++ b/lib/editor/atto/yui/build/moodle-editor_atto-editor/moodle-editor_atto-editor.js
@@ -737,37 +737,48 @@ EditorToolbarNav.prototype = {
         // Prevent the default browser behaviour.
         e.preventDefault();
 
-        var buttons = this.toolbar.all('button');
-
         // On cursor moves we loops through the buttons.
-        var found = false,
-            index = 0,
+        var buttons = this.toolbar.all('button'),
             direction = 1,
-            checkCount = 0,
-            group,
-            candidate,
             button,
             current = e.target.ancestor('button', true);
 
-        // Determine which button is currently selected.
-        while (!found && index < buttons.size()) {
-            if (buttons.item(index) === current) {
-                found = true;
-            } else {
-                index++;
-            }
-        }
-
-        if (!found) {
-            return;
-        }
-
         if (e.keyCode === 37) {
             // Moving left so reverse the direction.
             direction = -1;
         }
 
-        // Try to find the next
+        button = this._findFirstFocusable(buttons, current, direction);
+        if (button) {
+            button.focus();
+        } else {
+        }
+    },
+
+    /**
+     * Find the first focusable button.
+     *
+     * @param {NodeList} buttons A list of nodes.
+     * @param {Node} startAt The node in the list to start the search from.
+     * @param {Number} direction The direction in which to search (1 or -1).
+     * @return {Node | Undefined} The Node or undefined.
+     * @method _findFirstFocusable
+     * @private
+     */
+    _findFirstFocusable: function(buttons, startAt, direction) {
+        var checkCount = 0,
+            group,
+            candidate,
+            button,
+            index;
+
+        // Determine which button to start the search from.
+        index = buttons.indexOf(startAt);
+        if (index < -1) {
+            index = 0;
+        }
+
+        // Try to find the next.
         while (checkCount < buttons.size()) {
             index += direction;
             if (index < 0) {
@@ -798,11 +809,35 @@ EditorToolbarNav.prototype = {
             break;
         }
 
-        if (button) {
-            button.focus();
-            this._setTabFocus(button);
-        } else {
+        return button;
+    },
+
+    /**
+     * Check the tab focus.
+     *
+     * When we disable or hide a button, we should call this method to ensure that the
+     * focus is not currently set on an inaccessible button, otherwise tabbing to the toolbar
+     * would be impossible.
+     *
+     * @method checkTabFocus
+     * @chainable
+     */
+    checkTabFocus: function() {
+        if (this._tabFocus) {
+            if (this._tabFocus.hasAttribute('disabled') || this._tabFocus.hasAttribute('hidden')
+                    || this._tabFocus.ancestor('.atto_group').hasAttribute('hidden')) {
+                // Find first available button.
+                button = this._findFirstFocusable(this.toolbar.all('button'), this._tabFocus, -1);
+                if (button) {
+                    if (this._tabFocus.compareTo(document.activeElement)) {
+                        // We should also move the focus, because the inaccessible button also has the focus.
+                        button.focus();
+                    }
+                    this._setTabFocus(button);
+                }
+            }
         }
+        return this;
     },
 
     /**
diff --git a/lib/editor/atto/yui/build/moodle-editor_atto-plugin/moodle-editor_atto-plugin-debug.js b/lib/editor/atto/yui/build/moodle-editor_atto-plugin/moodle-editor_atto-plugin-debug.js
index 4e5a062add7..a35a28e3037 100644
--- a/lib/editor/atto/yui/build/moodle-editor_atto-plugin/moodle-editor_atto-plugin-debug.js
+++ b/lib/editor/atto/yui/build/moodle-editor_atto-plugin/moodle-editor_atto-plugin-debug.js
@@ -881,6 +881,7 @@ EditorPluginButtons.prototype = {
             }, this);
         }
 
+        this.get('host').checkTabFocus();
         return this;
     },
 
diff --git a/lib/editor/atto/yui/build/moodle-editor_atto-plugin/moodle-editor_atto-plugin-min.js b/lib/editor/atto/yui/build/moodle-editor_atto-plugin/moodle-editor_atto-plugin-min.js
index 30d52c5a8c8..757d58ee98f 100644
--- a/lib/editor/atto/yui/build/moodle-editor_atto-plugin/moodle-editor_atto-plugin-min.js
+++ b/lib/editor/atto/yui/build/moodle-editor_atto-plugin/moodle-editor_atto-plugin-min.js
@@ -1,2 +1,2 @@
 YUI.add("moodle-editor_atto-plugin",function(e,t){function n(){n.superclass.constructor.apply(this,arguments)}function c(){}function h(){}var r=".atto_group.",i="_group";e.extend(n,e.Base,{name:null,editor:null,toolbar:null,initializer:function(e){this.name=e.name,this.toolbar=e.toolbar,this.editor=e.editor,this.buttons={},this.buttonNames=[],this.buttonStates={},this.menus={},this._buttonHandlers=[],this._menuHideHandlers=[]},markUpdated:function(){return this.get("host").updateOriginal()}},{NAME:"editorPlugin",ATTRS:{host:{writeOnce:!0},group:{writeOnce:!0,getter:function(t){var n=this.toolbar.one(r+t+i);return n||(n=e.Node.create('<div class="atto_group '+t+i+'"></div>'),this.toolbar.append(n)),n}}}}),e.namespace("M.editor_atto").EditorPlugin=n;var s='<button class="{{buttonClass}} atto_hasmenu" tabindex="-1" type="button" title="{{title}}"><img class="icon" aria-hidden="true" role="presentation" width="16" height="16" style="background-color:{{config.menuColor}};" src="{{config.iconurl}}" /><img class="icon" aria-hidden="true" role="presentation" width="16" height="16" src="{{image_url "t/expanded" "moodle"}}"/></button>',o='<div class="{{config.buttonClass}} atto_menu" style="min-width:{{config.innerOverlayWidth}};"><ul class="menu">{{#each config.items}}<li role="presentation" class="atto_menuentry"><a href="#" role="menuitem" data-index="{{@index}}">{{{text}}}</a></li>{{/each}}</ul></div>',u="disabled",a="highlight",f="moodle-editor_atto-editor-plugin",l={EDITORWRAPPER:".editor_atto_content"};c.ATTRS={},c.prototype={buttons:null,buttonNames:null,buttonStates:null,menus:null,DISABLED:0,ENABLED:1,_buttonHandlers:null,_menuHideHandlers:null,addButton:function(t){var n=this.get("group"),r=this.name,i="atto_"+r+"_button",s,o=this.get("host");t.exec&&(i=i+"_"+t.exec),t.buttonName?i=i+"_"+t.buttonName:t.buttonName=t.exec||r,t=this._normalizeIcon(t),t.title||(t.title="pluginname");var u=M.util.get_string(t.title,"atto_"+r);s=e.Node.create('<button class="'+i+'"'+'tabindex="-1">'+'<img class="icon" aria-hidden="true" role="presentation" width="16" height="16" src="'+t.iconurl+'"/>'+"</button>"),s.setAttribute("title",u),n.append(s);var a=this.toolbar.getAttribute("aria-activedescendant");a||(s.setAttribute("tabindex","0"),this.toolbar.setAttribute("aria-activedescendant",s.generateID()),this.get("host")._tabFocus=s),t=this._normalizeCallback(t),this._buttonHandlers.push(this.toolbar.delegate("click",t.callback,"."+i,this)),t.keys&&this._addKeyboardListener(t.callback,t.keys,i);if(t.tags){var f=null;typeof t.tagMatchRequiresAll=="boolean"&&(f=t.tagMatchRequiresAll),this._buttonHandlers.push(o.on("atto:selectionchanged",function(e){o.selectionFilterMatches(t.tags,e.selectedNodes,f)?this.highlightButtons(t.buttonName):this.unHighlightButtons(t.buttonName)},this))}return this.buttonNames.push(t.buttonName),this.buttons[t.buttonName]=s,this.buttonStates[t.buttonName]=this.ENABLED,s},addBasicButton:function(e){return e.exec?(e.icon||(e.icon="e/"+e.exec),e.callback=function(){document.execCommand(e.exec,!1,null),this.markUpdated()},this.addButton(e)):null},addToolbarMenu:function(t){var n=this.get("group"),r=this.name,i="atto_"+r+"_button",o,u;t.buttonName?i=i+"_"+t.buttonName:t.buttonName=r,t=this._normalizeIcon(t),t.title||(t.title="pluginname");var a=M.util.get_string(t.title,"atto_"+r);t.menuColor||(t.menuColor="transparent");var f=e.Handlebars.compile(s);return o=e.Node.create(f({buttonClass:i,config:t,title:a})),n.append(o),u=this.toolbar.getAttribute("aria-activedescendant"),u||(o.setAttribute("tabindex","0"),this.toolbar.setAttribute("aria-activedescendant",o.generateID())),this._buttonHandlers.push(this.toolbar.delegate("click",this._showToolbarMenu,"."+i,this,t),this.toolbar.delegate("key",this._showToolbarMenu,"40, 32, enter","."+i,this,t)),this.buttonNames.push(t.buttonName),this.buttons[t.buttonName]=o,this.buttonStates[t.buttonName]=this.ENABLED,o},_showToolbarMenu:function(t,n){t.preventDefault();if(!this.isEnabled())return;if(t.currentTarget.ancestor("button",!0).hasAttribute(u))return;var r;if(!this.menus[n.buttonClass]){n.overlayWidth||(n.overlayWidth="14"),n.innerOverlayWidth||(n.innerOverlayWidth=parseInt(n.overlayWidth,10)-2+"em"),n.overlayWidth=parseInt(n.overlayWidth,10)+"em";var i=e.Handlebars.compile(o),s=e.Node.create(i({config:n}));this.menus[n.buttonClass]=new M.core.dialogue({bodyContent:s,width:null,visible:!1,center:!1,closeButton:!1,responsive:!1,extraClasses:["editor_atto_menu"]}),r=this.menus[n.buttonClass],r.headerNode.hide(),this._buttonHandlers.push(s.delegate("click",this._chooseMenuItem,".atto_menuentry a",this,n,r),s.delegate("key",this._chooseMenuItem,"32, enter",".atto_menuentry",this,n,r),s.delegate("key",this._menuKeyboardNavigation,"down:38,40",".menu",this),s.delegate("key",this._hideMenu,"down:37,39",".menu",this,r))}var a=this.buttons[n.buttonName];this.get("host")._setTabFocus(a),r=this.menus[n.buttonClass],r.set("focusAfterHide",a),r.show(),r.align(this.buttons[n.buttonName],[e.WidgetPositionAlign.TL,e.WidgetPositionAlign.BL]),r.get("boundingBox").one("a").focus(),this._menuHideHandlers.push(r.get("boundingBox").on("focusoutside",this._hideMenu,this,r))},_hideMenu:function(t,n){n.hide(),(new e.EventHandle(this._menuHideHandlers)).detach()},_chooseMenuItem:function(e,t,n){var r=e.target.ancestor("a",!0).getData("index"),i=this._normalizeCallback(t.items[r],t.globalItemConfig);n.set("focusAfterHide",null),i.callback(e,i._callback,i.callbackArgs)},_normalizeCallback:function(t,n){return t._callbackNormalized?t:(n||(n={}),typeof t.wrapCallback=="undefined"&&(t.wrapCallback=n.wrapCallback||!0),t.wrapCallback?(t._callback=t.callback||n.callback,t.callback=e.rbind(this._callbackWrapper,this,t._callback,t.callbackArgs)):t.callback=t.callback||n.callback,t._callbackNormalized=!0,t)},_normalizeIcon:function(e){return e.iconurl||(e.iconComponent||(e.iconComponent="core"),e.iconurl=M.util.image_url(e.icon,e.iconComponent)),e},_callbackWrapper:function(e,t,n){e
-.preventDefault();if(!this.isEnabled())return;var r=e.currentTarget.ancestor("button",!0);if(r&&r.hasAttribute(u))return;this.get("host").isActive()||this.get("host").focus(),r&&this.get("host")._setTabFocus(r);var i=[e,n];t.apply(this,i)},_addKeyboardListener:function(t,n,r){var i="key",s=l.EDITORWRAPPER,o;if(e.Lang.isArray(n))return e.Array.each(n,function(e){this._addKeyboardListener(t,e)},this),this;typeof n=="object"?(n.eventtype&&(i=n.eventtype),n.container&&(s=n.container),o=n.keyCodes):o=this._getKeyEvent()+n+this._getDefaultMetaKey(),this._buttonHandlers.push(this.editor.delegate(i,t,o,s,this))},isEnabled:function(){var t=e.Object.some(this.buttonStates,function(e){return e===this.ENABLED},this);return t},disableButtons:function(e){return this._setButtonState(!1,e)},enableButtons:function(e){return this._setButtonState(!0,e)},_setButtonState:function(t,n){var r="setAttribute";return t&&(r="removeAttribute"),n?this.buttons[n]&&(this.buttons[n][r](u,u),this.buttonStates[n]=t?this.ENABLED:this.DISABLED):e.Array.each(this.buttonNames,function(e){this.buttons[e][r](u,u),this.buttonStates[e]=t?this.ENABLED:this.DISABLED},this),this},highlightButtons:function(e){return this._changeButtonHighlight(!0,e)},unHighlightButtons:function(e){return this._changeButtonHighlight(!1,e)},_changeButtonHighlight:function(t,n){var r="addClass";return t||(r="removeClass"),n?this.buttons[n]&&this.buttons[n][r](a):e.Object.each(this.buttons,function(e){e[r](a)},this),this},_menuKeyboardNavigation:function(e){e.preventDefault();var t=e.currentTarget.all('a[role="menuitem"]'),n=!1,r=0,i=1,s=0,o=e.target.ancestor('a[role="menuitem"]',!0);while(!n&&r<t.size())t.item(r)===o?n=!0:r++;if(!n)return;e.keyCode===38&&(i=-1);do r+=i,r<0?r=t.size()-1:r>=t.size()&&(r=0),next=t.item(r),s++;while(s<t.size()&&next!==o&&next.hasAttribute("hidden"));next&&next.focus()},_getDefaultMetaKey:function(){return e.UA.os==="macintosh"?"+meta":"+ctrl"},_getKeyEvent:function(){return"down:"}},e.Base.mix(e.M.editor_atto.EditorPlugin,[c]),h.ATTRS={},h.prototype={_dialogue:null,getDialogue:function(t){t=t||{};var n=!1;t.focusAfterHide&&(n=t.focusAfterHide,delete t.focusAfterHide);if(!this._dialogue){var r=e.merge({visible:!1,modal:!0,close:!0,draggable:!0},t);this._dialogue=new M.core.dialogue(r)}return n!==!1&&(n===!0?this._dialogue.set("focusAfterHide",this.buttons[this.buttonNames[0]]):typeof setFocusAfter=="string"?this._dialogue.set("focusAfterHide",this.buttons[n]):this._dialogue.set("focusAfterHide",n)),this._dialogue}},e.Base.mix(e.M.editor_atto.EditorPlugin,[h])},"@VERSION@",{requires:["node","base","escape","event","event-outside","handlebars","event-custom"]});
+.preventDefault();if(!this.isEnabled())return;var r=e.currentTarget.ancestor("button",!0);if(r&&r.hasAttribute(u))return;this.get("host").isActive()||this.get("host").focus(),r&&this.get("host")._setTabFocus(r);var i=[e,n];t.apply(this,i)},_addKeyboardListener:function(t,n,r){var i="key",s=l.EDITORWRAPPER,o;if(e.Lang.isArray(n))return e.Array.each(n,function(e){this._addKeyboardListener(t,e)},this),this;typeof n=="object"?(n.eventtype&&(i=n.eventtype),n.container&&(s=n.container),o=n.keyCodes):o=this._getKeyEvent()+n+this._getDefaultMetaKey(),this._buttonHandlers.push(this.editor.delegate(i,t,o,s,this))},isEnabled:function(){var t=e.Object.some(this.buttonStates,function(e){return e===this.ENABLED},this);return t},disableButtons:function(e){return this._setButtonState(!1,e)},enableButtons:function(e){return this._setButtonState(!0,e)},_setButtonState:function(t,n){var r="setAttribute";return t&&(r="removeAttribute"),n?this.buttons[n]&&(this.buttons[n][r](u,u),this.buttonStates[n]=t?this.ENABLED:this.DISABLED):e.Array.each(this.buttonNames,function(e){this.buttons[e][r](u,u),this.buttonStates[e]=t?this.ENABLED:this.DISABLED},this),this.get("host").checkTabFocus(),this},highlightButtons:function(e){return this._changeButtonHighlight(!0,e)},unHighlightButtons:function(e){return this._changeButtonHighlight(!1,e)},_changeButtonHighlight:function(t,n){var r="addClass";return t||(r="removeClass"),n?this.buttons[n]&&this.buttons[n][r](a):e.Object.each(this.buttons,function(e){e[r](a)},this),this},_menuKeyboardNavigation:function(e){e.preventDefault();var t=e.currentTarget.all('a[role="menuitem"]'),n=!1,r=0,i=1,s=0,o=e.target.ancestor('a[role="menuitem"]',!0);while(!n&&r<t.size())t.item(r)===o?n=!0:r++;if(!n)return;e.keyCode===38&&(i=-1);do r+=i,r<0?r=t.size()-1:r>=t.size()&&(r=0),next=t.item(r),s++;while(s<t.size()&&next!==o&&next.hasAttribute("hidden"));next&&next.focus()},_getDefaultMetaKey:function(){return e.UA.os==="macintosh"?"+meta":"+ctrl"},_getKeyEvent:function(){return"down:"}},e.Base.mix(e.M.editor_atto.EditorPlugin,[c]),h.ATTRS={},h.prototype={_dialogue:null,getDialogue:function(t){t=t||{};var n=!1;t.focusAfterHide&&(n=t.focusAfterHide,delete t.focusAfterHide);if(!this._dialogue){var r=e.merge({visible:!1,modal:!0,close:!0,draggable:!0},t);this._dialogue=new M.core.dialogue(r)}return n!==!1&&(n===!0?this._dialogue.set("focusAfterHide",this.buttons[this.buttonNames[0]]):typeof setFocusAfter=="string"?this._dialogue.set("focusAfterHide",this.buttons[n]):this._dialogue.set("focusAfterHide",n)),this._dialogue}},e.Base.mix(e.M.editor_atto.EditorPlugin,[h])},"@VERSION@",{requires:["node","base","escape","event","event-outside","handlebars","event-custom"]});
diff --git a/lib/editor/atto/yui/build/moodle-editor_atto-plugin/moodle-editor_atto-plugin.js b/lib/editor/atto/yui/build/moodle-editor_atto-plugin/moodle-editor_atto-plugin.js
index 911a37ac41d..039dc7a2374 100644
--- a/lib/editor/atto/yui/build/moodle-editor_atto-plugin/moodle-editor_atto-plugin.js
+++ b/lib/editor/atto/yui/build/moodle-editor_atto-plugin/moodle-editor_atto-plugin.js
@@ -877,6 +877,7 @@ EditorPluginButtons.prototype = {
             }, this);
         }
 
+        this.get('host').checkTabFocus();
         return this;
     },
 
diff --git a/lib/editor/atto/yui/src/editor/js/editor-plugin-buttons.js b/lib/editor/atto/yui/src/editor/js/editor-plugin-buttons.js
index 0763f802387..fe9db6ddce7 100644
--- a/lib/editor/atto/yui/src/editor/js/editor-plugin-buttons.js
+++ b/lib/editor/atto/yui/src/editor/js/editor-plugin-buttons.js
@@ -739,6 +739,7 @@ EditorPluginButtons.prototype = {
             }, this);
         }
 
+        this.get('host').checkTabFocus();
         return this;
     },
 
diff --git a/lib/editor/atto/yui/src/editor/js/toolbar-keyboardnav.js b/lib/editor/atto/yui/src/editor/js/toolbar-keyboardnav.js
index 4b892b607af..3c6dd30ab81 100644
--- a/lib/editor/atto/yui/src/editor/js/toolbar-keyboardnav.js
+++ b/lib/editor/atto/yui/src/editor/js/toolbar-keyboardnav.js
@@ -70,38 +70,50 @@ EditorToolbarNav.prototype = {
         // Prevent the default browser behaviour.
         e.preventDefault();
 
-        var buttons = this.toolbar.all('button');
-
         // On cursor moves we loops through the buttons.
-        var found = false,
-            index = 0,
+        var buttons = this.toolbar.all('button'),
             direction = 1,
-            checkCount = 0,
-            group,
-            candidate,
             button,
             current = e.target.ancestor('button', true);
 
-        // Determine which button is currently selected.
-        while (!found && index < buttons.size()) {
-            if (buttons.item(index) === current) {
-                found = true;
-            } else {
-                index++;
-            }
-        }
-
-        if (!found) {
-            Y.log("Unable to find this button in the list of buttons", 'debug', LOGNAME);
-            return;
-        }
-
         if (e.keyCode === 37) {
             // Moving left so reverse the direction.
             direction = -1;
         }
 
-        // Try to find the next
+        button = this._findFirstFocusable(buttons, current, direction);
+        if (button) {
+            button.focus();
+        } else {
+            Y.log("Unable to find a button to focus on", 'debug', LOGNAME);
+        }
+    },
+
+    /**
+     * Find the first focusable button.
+     *
+     * @param {NodeList} buttons A list of nodes.
+     * @param {Node} startAt The node in the list to start the search from.
+     * @param {Number} direction The direction in which to search (1 or -1).
+     * @return {Node | Undefined} The Node or undefined.
+     * @method _findFirstFocusable
+     * @private
+     */
+    _findFirstFocusable: function(buttons, startAt, direction) {
+        var checkCount = 0,
+            group,
+            candidate,
+            button,
+            index;
+
+        // Determine which button to start the search from.
+        index = buttons.indexOf(startAt);
+        if (index < -1) {
+            Y.log("Unable to find the button in the list of buttons", 'debug', LOGNAME);
+            index = 0;
+        }
+
+        // Try to find the next.
         while (checkCount < buttons.size()) {
             index += direction;
             if (index < 0) {
@@ -132,12 +144,35 @@ EditorToolbarNav.prototype = {
             break;
         }
 
-        if (button) {
-            button.focus();
-            this._setTabFocus(button);
-        } else {
-            Y.log("Unable to find a button to focus on", 'debug', LOGNAME);
+        return button;
+    },
+
+    /**
+     * Check the tab focus.
+     *
+     * When we disable or hide a button, we should call this method to ensure that the
+     * focus is not currently set on an inaccessible button, otherwise tabbing to the toolbar
+     * would be impossible.
+     *
+     * @method checkTabFocus
+     * @chainable
+     */
+    checkTabFocus: function() {
+        if (this._tabFocus) {
+            if (this._tabFocus.hasAttribute('disabled') || this._tabFocus.hasAttribute('hidden')
+                    || this._tabFocus.ancestor('.atto_group').hasAttribute('hidden')) {
+                // Find first available button.
+                button = this._findFirstFocusable(this.toolbar.all('button'), this._tabFocus, -1);
+                if (button) {
+                    if (this._tabFocus.compareTo(document.activeElement)) {
+                        // We should also move the focus, because the inaccessible button also has the focus.
+                        button.focus();
+                    }
+                    this._setTabFocus(button);
+                }
+            }
         }
+        return this;
     },
 
     /**