"Gecko's GTK/GDK X11 port uses some features of the GDK X11 backend, so porting to GTK3 is only part of work required for a GTK/Wayland port." - https://bugzilla.mozilla.org/show_bug.cgi?id=627699#c65
Originally Posted by Khudsa
In addition to the GTK2 stuff firefox used which is related to this bug, there is some xlib stuff firefox uses which will still be a problem as a wayland client after this bug is closed.
There is another bug specifically for wayland support: https://bugzilla.mozilla.org/show_bug.cgi?id=635134
It hasn't gotten much love.
There is also their new servo engine, which also has a bug for wayland support, but that seems pretty far off from being usable: https://github.com/mozilla/servo/issues/332