Autocomplete foo.

toolkit/content/widgets/autocomplete.xml

@@ -305,6 +305,7 @@
                 break;
               case KeyEvent.DOM_VK_DOWN:
                 cancel = this.mController.handleKeyNavigation(IController.KEY_DOWN);
+                aEvent.preventBubble();
                 break;
               case KeyEvent.DOM_VK_LEFT:
                 cancel = this.mController.handleKeyNavigation(IController.KEY_LEFT);

toolkit/skin/unix/autocomplete.css

@@ -98,6 +98,7 @@ textbox {
 /* ::::: tree ::::: */
 
 .autocomplete-tree {
+  -moz-appearance: none !important;
   border: none;
   background-color: transparent !important;
 }