Followup to checkin for 116653 (openURL(,new-tab) support). Seems that the

observer service doesn't implement classinfo, and some people were reporting
a strict warning (?) related to this.  This is a more correct approach anyway,
so here we go. r=blizzard, sr=jag.

xpfe/browser/resources/content/navigator.js

@@ -304,8 +304,8 @@ function RegisterTabOpenObserver()
     }
   };
 
-  const service =
-    Components.classes["@mozilla.org/observer-service;1"].getService();
+  const service = Components.classes["@mozilla.org/observer-service;1"]
+    .getService(Components.interfaces.nsIObserverService);
   service.addObserver(observer, "open-new-tab-request", false);
 }