Fedora 31 Workstation comes with a Firefox backend moved from X11 to Wayland by default. That’s just another step in the ongoing effort of moving to Wayland. This affects GNOME on Wayland only. This article helps you understand some changes and extra steps you may wish to take depending on your preferences.
There is a firefox-wayland package available to activate the Wayland backend on KDE and Sway desktop environments.
The Wayland architecture is completely different than X11. The team merged various aspects of Firefox internals to the new protocol where possible. However, some X11 features are missing completely. For such cases you can install and run firefox-x11 package as a fallback.
If you want to run the Flash plugin, you must install the firefox-x11 package, since Flash requires X11 and GTK 2. Wayland also has a slightly different drag and drop behavior and strict popup window hierarchy.
Generally, if you think Firefox is not behaving like you want, try the firefox-x11 package. In this case, ideally you should report the misbehavior in Bugzilla.
The Wayland architecture comes with many benefits, and overcomes many limitations of X11. For instance, it can deliver smoother rendering and better HiDPI and screen scale support. You can also enable EGL hardware acceleration on Intel and AMD graphics cards. This decreases your power consumption and also gives you partially accelerated video playback. To enable it, navigate to about:config, and search for layers.acceleration.force-enabled. Set this option to true and restart Firefox.
Brave users may wish to try the Firefox next-generation renderer, called WebRender, written in Rust. To do that, search for gfx.webrender.enabled and gfx.webrender.all in about:config. Set them to true, then cross your fingers and restart Firefox.
But don’t worry — even if Firefox crashes at start after these experiments, you can launch it in safe mode to reset these options. Start Firefox from a terminal using the following command:
$ firefox -safe-mode