I’ve exclusively used firefox to watch youtube on Arch and Ubuntu for years, never had a problem so far for what it’s worth. I keep a laptop in the livingroom with Arch specifically to have adblocking and piping the video out to the TV. The youtube apps are terrible on the Roku last I remember, haven’t tried it in forever but I think the main reason was I didn’t want to see ads anymore.

FF has way too much groundwork laid and way too much mindshare currently (especially given the rust language and all…) If, for some reason, thousands of devs just gave up on mozilla, more would continue the path and fork it most likely.