Landing bug 352323 (the scroll right button doesn't appear disabled like the scroll left, patch by Seth Spitzer, r=mconnor) scrollbox.xml portion on trunk, the tabbrowser/theme portions were landed as as part of bug 353673).

toolkit/content/widgets/scrollbox.xml

@@ -152,6 +152,10 @@
 
           this._scrollButtonUp.disabled = disableUpButton;
           this._scrollButtonDown.disabled = disableDownButton;
+
+          var event = document.createEvent("Events");
+          event.initEvent("UpdatedScrollButtonsDisabledState", true, false);
+          this.dispatchEvent(event);                                            
         ]]></body>
       </method>
     </implementation>