What setting is this? Afaik there is hardware accelerated drawing, but no VAAPI. There used to be some kludge back when gstreamer was the backend, but I’m pretty sure it doesn’t work now we’re using FFmpeg.
Sorry you're right. I thought parent was refering to accelerated drawing, not decoding. That said, for my use case, this is all I need on a work laptop. My desktop CPU doesn't break a sweat on software decoding, so I'm not too bothered.
It doesn't work on linux installations I've had around. The experience of watching in-browser videos on linux is too poor to bother with (it's hot enough as is in an Australian summer). I either download (youtube-dl etc) or use my tablet (for smaller ad hoc things) instead.
I think it's unstable. I had to disable it because it was causing frequent reboots that wouldn't stop until the computer was powered off long enough that the memory cleared out. Even if I booted into Windows after the forced reboot, it would still continually reboot. I don't know what the issue was, but it stopped after disabling hardware acceleration.
Most likely patents. Firefox only has video acceleration on Windows if you have codecs installed already (because the codec people paid the patent license fees) and the acceleration relies entirely on the codec+driver combo.
Chrome ships libavcodec/ffmpeg bits because they've paid the license fees.