Has anyone gotten VA-API hardware acceleration working in Firefox?

Hi,
I’ve followed the instructions on the Arch Wiki and still see ~150% CPU usage on one core while watching a video, for example on YouTube. Is there a reason the VAAPI acceleration that should work on Wayland (and soon, FF 80, on X11) doesn’t work on a 15v4?

Have you been able to figure it out? It’d be great to see CPU usage at ~20% for my highest usage core, as I do when watching via VLC.