MDL-50685 core_form: disable hidden options, don't just hide

lib/form/searchableselector.js

@@ -90,9 +90,11 @@ selector = {
         if (selector.goodbrowser) {
             if (visible) {
                 element.style.display = 'block';
+                element.disabled = false;
             } else {
                 element.style.display = 'none';
                 element.selected = false;
+                element.disabled = true;
             }
         } else {
             // This is a deeply evil hack to make the filtering work in IE.
@@ -103,7 +105,7 @@ selector = {
                 if (element.parentNode.tagName.toLowerCase() === 'span') {
                     element.parentNode.parentNode.replaceChild(element, element.parentNode); // New, old.
                 }
-                element.enabled = true;
+                element.disabled = false;
             } else {
                 if (element.parentNode.tagName.toLowerCase() !== 'span') {
                     var span = document.createElement('span');
@@ -111,7 +113,7 @@ selector = {
                     span.appendChild(element);
                     span.style.display = 'none';
                 }
-                element.enabled = false;
+                element.disabled = true;
                 element.selected = false;
             }
         }