These are very different experiences we have. I've been using FF on Linux and on Windows since before the first day I found Youtube, and have not yet had a period where it doesn't work.
It's not pretending when tens of thousands are browsing that self-same site just fine over the period you had problems.
I've used Debian, Mint, Ubuntu, Fedora, Arch, Slackware and more. In none of them did I need to do anything specific to make FF work on youtube.
What am I doing wrong? All the games I want to play just seem to work without issue, including new AAA titles, with exceptions for things that use kernel level anticheat that I wouldn't play anyway specifically because of that.
Arc Raiders, Helldivers 2, Factorio, etc just fine. I'm even involved in some alpha / beta testing for a couple of new games.
Just running fedora + proton (wine). I just use the regular steam client like anyone else.