fune/browser/base/content/test/general/browser_bug609700.js

function test() {
  waitForExplicitFinish();

  Services.ww.registerNotification(function notification(aSubject, aTopic, aData) {
    if (aTopic == "domwindowopened") {
      Services.ww.unregisterNotification(notification);

      ok(true, "duplicateTabIn opened a new window");

      whenDelayedStartupFinished(aSubject, function() {
        executeSoon(function() {
          aSubject.close();
          finish();
        });
      }, false);
    }
  });

  duplicateTabIn(gBrowser.selectedTab, "window");
}