browser/components/customizableui/test/browser_940307_panel_click_closure_handling.js fails after bug 1193394, because it tries to open popup which state is "hiding" https://treeherder.mozilla.org/#/jobs?repo=try&revision=17fca1f2db86843ce54c307cbf4fefd7f6b3936f&group_state=expanded&selectedJob=151164062 > TEST-UNEXPECTED-FAIL | browser/components/customizableui/test/browser_940307_panel_click_closure_handling.js | Test timed out - > TEST-UNEXPECTED-FAIL | browser/components/customizableui/test/browser_940307_panel_click_closure_handling.js | Uncaught exception received from previously timed out test - at chrome://mochitests/content/browser/browser/components/customizableui/test/browser_940307_panel_click_closure_handling.js:88 - TypeError: EventUtils.synthesizeMouseAtCenter is not a function > Stack trace: > disabled_button_in_panel@chrome://mochitests/content/browser/browser/components/customizableui/test/browser_940307_panel_click_closure_handling.js:88:3 > Async*Tester_execTest/<@chrome://mochikit/content/browser-test.js:1065:21 > Tester_execTest@chrome://mochikit/content/browser-test.js:1056:9 > Tester.prototype.nextTest</<@chrome://mochikit/content/browser-test.js:956:9 > SimpleTest.waitForFocus/waitForFocusInner/focusedOrLoaded/<@chrome://mochikit/content/tests/SimpleTest/SimpleTest.js:795:59 promisePanelElementHidden should wait for the next event tick before resolving the promise inside popuphidden event handler.

Just like other bugs, added executeSoon to wait for the next event tick, to make sure the other event listeners finish

https://hg.mozilla.org/integration/mozilla-inbound/rev/702bbe31b754068334b1f64c6b7195876a6b2921 Bug 1424877 - Wait for the next event tick in promisePanelElementHidden in browser/components/customizableui/test/head.js. r=Gijs