Bug 993712 - Try to fix permanent orange in browser_984455_bookmarks_items_reparenting.js by making sure test for 968447 fully closes its window. r=jaws.

browser/components/customizableui/test/browser_968447_bookmarks_toolbar_items_in_panel.js

@@ -27,6 +27,6 @@ add_task(function() {
   is(newWinBookmarksToolbarPlaceholder.getAttribute("wrap"), "true",
      "Button in new window should have 'wrap' attribute");
   yield newWin.PanelUI.hide();
-  newWin.close();
+  yield promiseWindowClosed(newWin);
   CustomizableUI.reset();
 });