Missed this post until now. I’d add the following to /etc/environment:
MOZ_ENABLE_WAYLAND=1
Otherwise Firefox-based browsers and Thunderbird won’t use Wayland. Also check whether qt5-wayland is installed, not sure whether this is on our package list already. The following to /etc/environment as well:
QT_QPA_PLATFORM="wayland;xcb"
That should be the most important.