It's still a real pain to get hardware accelerated video in a browser on Linux. Google is still outright refusing to support it in chromium, even though they do support it inside Chrome OS. There are few community patches floating around if you're willing to roll your own chromium to enable to Chrome OS hardware decode pathways on generic Linux.

You can mostly get it working on Firefox if you play around with the config options, but it only works with AMD and Intel GPUs (anything supporting vaapi).