For what it's worth, starting with firefox 65 there are two packages:
firefox-wayland-65.0-1.fc29.x86_64
firefox-65.0-1.fc29.x86_64
And after installing them there are two application icons in gnome:
Firefox and Firefox on Wayland. Both work fine when I've logged into a
gnome wayland session; and if it's a gnome on Xorg session, only
Firefox launches, whereas Firefox on Wayland sorta just fails silently
(spinner hangs out for a bit then goes away), there is a journal
message 'firefox[13165]: cannot open display: :0' but that's it.
https://bugzilla.redhat.com/show_bug.cgi?id=1671634
Chris Murphy