diff --git a/toolkit/content/widgets/autocomplete.xml b/toolkit/content/widgets/autocomplete.xml
index cbcf86f8347f..3f47cefe9fd6 100644
--- a/toolkit/content/widgets/autocomplete.xml
+++ b/toolkit/content/widgets/autocomplete.xml
@@ -877,11 +877,6 @@
         var controller = this.view.QueryInterface(Components.interfaces.nsIAutoCompleteController);
         controller.stopSearch();
 
-        // when the popup hides, we need to clear the selection
-        // otherwise we will use the value of the selected index when the
-        // user hits enter.
-        // see bug #400671 for details
-        this.selectedIndex = -1;
         this.mPopupOpen = false;
 
         // Reset the maxRows property to the cached "normal" value, and reset
@@ -953,10 +948,11 @@
           <![CDATA[
           if (!this.mPopupOpen) {
             this.mInput = aInput;
+            // clear any previous selection, see bugs 400671 and 488357
+            this.selectedIndex = -1;
             document.popupNode = null;
 
-            var rect = aElement.getBoundingClientRect();
-            var width = rect.right - rect.left;
+            var width = aElement.getBoundingClientRect().width;
             this.setAttribute("width", width > 100 ? width : 100);
             // invalidate() depends on the width attribute
             this._invalidate();
diff --git a/toolkit/content/widgets/listbox.xml b/toolkit/content/widgets/listbox.xml
index 5b0082b1816c..63ef676f93ef 100644
--- a/toolkit/content/widgets/listbox.xml
+++ b/toolkit/content/widgets/listbox.xml
@@ -398,7 +398,7 @@
             for (var i = this.selectedItems.length - 1; i >= 0; --i)
               this.selectedItems[i].selected = false;
 
-            this.selectedItems.splice(0, this.selectedItems.length);
+            this.selectedItems.length = 0;
           }
 
           this._selectionStart = null;