It's kind of depressing to see otherwise tech-capable folks go "Firefox is so bad, Youtube is absurdly slow all the time" and not for a moment consider that maybe the problem there isn't actually Firefox, but rather the video site famously owned by an anti-competitive monopolist that also owns the most popular browser and so has a *direct interest* in making it slow on Firefox.
Apparently Google's campaign of "only optimizing for Chrome" is working. Fucking hell.