That's the only reason I am not switching to FF 100%. I do use it though but not as a main driver.
Some of the related posts:
https://www.zdnet.com/article/youtube-is-slowing-video-loads...
I keep retrying Firefox over multiple years and it's still not quite equal to Chrome for Youtube 4k playback ...
2021: https://news.ycombinator.com/item?id=28783904
2024: https://news.ycombinator.com/item?id=42176450
2026 still talks about the problem: https://go.tabbit.ai/blog/firefox-youtube-4k-stuttering
And a recent Youtube comment (2026-September) notices that Firefox doesn't run as well as Chrome on his modern high-end laptop with 64GB RAM: https://www.youtube.com/watch?v=vIE_PkuFeng&lc=UgxfGeBL6sopr...
If FF is not working on youtube for, it's not working for you and you alone.
I stopped using Brave for no reason i don't remember. (no, not to do with the CEO)
I generally use Safari on my Apple devices (and YT works) and Firefox on any Linux machines. If something does not work on Safari I try Firefox on my Mac. In the past I've also sometimes used Chrome when no other option works.
So one option could be to use Firefox as a 'general use' browser, and switch to something else on an as-needed basis.
A bit of a hassle, but it may be the best compromise currently.
You must have a hardware problem, as I'm playing 4K videos on a 1st-gen Ryzen and GTX 1080 using Firefox and I've never had a single issue since I got the machine, around the 4th week the processor was available to purchase.
I am perfectly happy with Chrome.
Really well argued, congrats.