Wayland Firefox: For me, it doesn't work at all with scaling, and on another machine with no scaling, opening new window (in the sense of a new wayland surface, so that includes dialogs) could take 30-60 seconds, during which Firefox would be completely unresponsive (this was fixed in v65 yesterday).

Hw accelerated videos: some distributions (fedora, suse, arch?) have patched Chromium with VA-API support. On some GPUs, the allow_rgb10_configs raises it's ugly head though. In also works only in native X11, not in Xwayland. Other than that, it is only way to watch youtube during the more intensive compiles :)