Firefox 84.0 is a big milestone for Firefox Linux development as it comes with HW acceleration by default for some Linux users. Stock Mozilla Firefox 84.0 enables WebRender (HW accelerated backend) for Gnome/X.org and Gnome/Wayland will be supported in Firefox 85.0. Fedora is bit ahead and enables WebRender for Gnome/Wayland in Firefox 84.0 too.
WebRender by default is restricted to AMD/Intel graphics cards as NVIDIA is known for various issues – both proprietary and Noveau drivers.
And why it’s enabled in Gnome only for now? For instance KDE is also a popular desktop environment. I think it’s because Gnome utilizes HW acceleration so when Gnome works on your box there’s assumption that Firefox will work too. KDE provides choices how to disable/restrict HW acceleration setup (for instance it supports disabled screen compositing) and it’s more difficult to cover various scenarios.
Another excluded group are XWayland users. It means you have Wayland as a desktop compositor but for some reasons you use X11 emulation layer and run Firefox as X11 application. It’s a valid scenario, Firefox with Wayland backend still suffers from some annoying bug, mostly related to popup windows.
But don’t worry, Mozilla folks are going to bring WebRender to the most Linux users on various desktops and graphics. Jan created a brief Linux WebRender state overview. And you can help with it! Please check if you have WebRender enabled and eventually try to enable it. Test various web pages, video playback, WebGL and report your experience. You can use comments below or drop me a mail at firstname.lastname@example.org.