[twistedcheeslet]

From my experience hardware acceleration has been quite lacking on Ubuntu (especially noticeable when watching YouTube).

[puzzlingcaptcha]

VA-API has been enabled by default for linux builds in Firefox 115 (at least for Intel GPUs).

Keep in mind you also need to have the intel-media-driver installed (for Broadwell+)

[jeroenhd]

If you use an Nvidia GPU (i.e. a gaming machine or ML desktop) you'll have to force a whole bunch of settings to use it through a compatibility layer that isn't particularly stable, or accept the CPU hit of about 1 core per video file at 1080p. It's not unusable but very annoying when the fallback behaviour accidentally triggers on a laptop and your CPU ends up constantly boosting, draining the battery.

Firefox on my Intel iGPU + Nvidia dGPU likes to pretend the iGPU doesn't exist. Very annoying but I've given up on trying to get it to work on desktop. Chrome seems to do a lot better for somme reason.

[danogentili]

It just needs a little bit of configuration in the about:config tab, it works just fine with VAAPI!