As a next step in the Wayland effort we have new fresh Firefox packages  with all the goodies from Firefox 63/64 (Nightly) for you. They come with better (and fixed) rendering, v-sync support, and working HiDPI. Support for hi-res displays is not perfect yet and more fixes are on the way – thanks to Jan Horak who wrote that patches.
The builds also ship PipeWire WebRTC patch for desktop sharing created by Jan Grulich and Tomas Popela. Wayland applications are isolated from desktop and don’t have access to other windows (as X11) thus PipeWire supplies the missing functionality along the browser sandbox.
I think the rendering is generally covered now and the browser should work smoothly with Wayland backend. That’s also a reason why I make it default on Fedora 30 (Rawhide) and firefox-x11 package is available as a X11 fallback. Fedora 29 and earlier stay with default X11 backend and Wayland is provided by firefox-wayland package.