Has worked reliably for years until two weeks ago when I downloaded a now-banned video. I can no longer see the download button. Since then, I have tried to use other YouTube download add-ons, but they do not work either, so maybe the problem is on the Mozilla side or YouTube side. I see that there are "Mozilla recommended" add-ons, but they require invasive levels of permissions.
UPDATE: I uninstalled and reinstalled. Now working. (Disable-/re-enable did NOT work).
Piece of shit that creates popups like https://browser-games.xyz/game.php?id=16&utm_source=en_extensions&utm_medium=sry_page&lang=en&source_type=uninstall&cid=ntpromo_yd_store&ext=YouTube%20Downloader.