Bug 309289: When moving an extension up/down in the richlistbox widget, it is scrolled to the top of the window, patch by Simon B�nzli <zeniko@gmail.com>, r=mconnor/doron

toolkit/content/widgets/richlistbox.xml

@@ -128,7 +128,8 @@
 
               if (element) {
                 this.selectedItem = element;
-                this.scrollBoxObject.scrollToElement(this.selectedItem);
+                if (!this._isItemVisible(this.selectedItem))
+                  this.scrollBoxObject.scrollToElement(this.selectedItem);
                 return;
               }
             }