I'm so tired of this bug, sorry that it affects you. The best we can do right now is wait for someone to finish submitting a patch for this bug, since it's a Firefox issue: https://bugzilla.mozilla.org/show_bug.cgi?id=1324255

If you're comfortable with coding and building an npm project, you can try: you can try extending the timeout values in this function https://github.com/reblws/tab-search/blob/master/src/core/pages/popup/side-effects.js#L81in focusSearchInputWorkaround and see if that might help.