The Tor Browser / file revision

 function test() {

   var contentWin = window.open("about:blank", "", "width=100,height=100");

   var enumerator = Services.wm.getEnumerator("navigator:browser");

   while (enumerator.hasMoreElements()) {

     let win = enumerator.getNext();

     if (win.content == contentWin) {

       gPrefService.setBoolPref("browser.tabs.closeWindowWithLastTab", false);

       win.gBrowser.removeCurrentTab();

       ok(win.closed, "popup is closed");

       // clean up

       if (!win.closed)

         win.close();

       if (gPrefService.prefHasUserValue("browser.tabs.closeWindowWithLastTab"))

         gPrefService.clearUserPref("browser.tabs.closeWindowWithLastTab");

       return;

     }

   }

   throw "couldn't find the content window";

 }