I wanted to test out WebRender in Firefox now that it’s on the brink of being turned on by default in GNOME environments. Despite enabling gfx.webrender.all, about:support showed that WebRender wasn’t working and reported errors including Failed to load EGL library: FEATURE_FAILURE_EGL_LOAD_3 and Failed GL context creation for WebRender.
Fixing this in my environment (Fedora 33, KDE Plasma 5.20, X11, AMD Mesa) came down to simply installing libglvnd-gles.
I’m not sure if this is required for other hardware configurations or desktop environments or under Wayland. I like trying out the latter with each KDE Plasma release, but while things seem to be getting better, the number of crashes still makes it feel very far from being ready for prime time.
VA-API hardware video acceleration
A significant advantage of WebRender is that it enables support for VA-API hardware video acceleration. Just set flags media.ffmpeg.vaapi.enabled to true, media.ffvpx.enabled to false and environment variable MOZ_X11_EGL to 1 to give your CPU a nice rest.
In related news, I’m excited to see progress on this long-standing bug that should mean VLC’s VA-API option actually works under AMD Mesa. (Update: Mesa 20.3.2 is available for testing, and it’s working well.)