Bug 740974 - toolbar currentSet setter needs to return 'val' when returning early. r=dao

toolkit/content/widgets/toolbar.xml

@@ -225,7 +225,7 @@
         <setter>
           <![CDATA[
             if (val == this.currentSet)
-              return;
+              return val;
 
             var ids = (val == "__empty") ? [] : val.split(",");