Fix bustage from bug 802026, a=me

browser/base/content/test/browser_URLBarSetURI.js

@@ -37,7 +37,7 @@ let tests = [
     });
   },
   function customize(next) {
-    whenNewWindowLoaded(null, function (win) {
+    whenNewWindowLoaded(undefined, function (win) {
       // Need to wait for delayedStartup for the customization part of the test,
       // since that's where BrowserToolboxCustomizeDone is set.
       whenDelayedStartupFinished(win, function () {