Can’t speak for all users, but at least as of about six months ago, there appears to be a bug in Firefox in NixOS where the shader cache doesn’t appear to be able to write properly, and as such video acceleration doesn’t work. It became most evident when I was trying to watch 360-degree videos in Immich.

Entirely possible that this is an issue specific to NixOS or my machine, but because of that issue I switched over to Brave.

I would like to go back to Firefox at some point. Maybe I’ll see if I can make a patch to fix video acceleration on NixOS.

the obvious thing to do is keep using firefox as your daily driver, and load up the other browser as needed for the video etc.

I'm being tongue-in-cheek here because it seems most people just give up on safari/firefox if one thing doesn't work and go to some chromium-based browser as their default driver. That's sad.