Bug 752389 - Launching any application attaches a /undefined to the end of the URL. r=fabrice

dom/base/Webapps.jsm

@@ -467,8 +467,9 @@ DOMApplicationManifest.prototype = {
   },
   
   fullLaunchPath: function(aStartPoint) {
+    let startPoint = aStartPoint || "";
     let launchPath = this._localeProp("launch_path") || "";
-    return this._origin.resolve(launchPath + aStartPoint);
+    return this._origin.resolve(launchPath + startPoint);
   }
 }