The extension stopped working due to youtube getting more bloated and slower every update, making the function fire before the miniplayer loads fully, I addressed the issue in the last patch, now it should work almost* always. If you're looking for an extension that wasn't coded at 3am with minimal effort because of a grudge against YT, checkout: https://addons.mozilla.org/en-US/firefox/addon/dopamine-free-youtube/ . An extension that I actually put some time into maintaining. (and it even blocks the miniplayer as well). But thanks for the review/feedback, haven't noticed it stopped working.