The leak I can reproduce locally somewhat often is coming from https://searchfox.org/mozilla-central/rev/08c493902519265d570250c8e7ce575c8cd6f5b5/browser/components/extensions/test/browser/browser_ext_windows_create_cookieStoreId.js#308,319-321 When adopting a tab to a new window, there is internally a frameloader swap. The initial frameloader is loading about:blank and after the old window has started to close https://searchfox.org/mozilla-central/rev/08c493902519265d570250c8e7ce575c8cd6f5b5/browser/actors/AboutReaderParent.jsm#156 triggers a call to extension code where getId is called. The failure becomes almost perma-fail with bug 1727829. Will push this with bug 1727829 to tryserver. Differential Revision: https://phabricator.services.mozilla.com/D124958
1708243
