Its even worse when you force Firefox to use wayland its icon doesn't even show.
Edit: Oh since everyone now is confused; I only have the flatpak version of Firefox installed yet it doesn't use the pinned icon and doesn't even use the firefox icon under wayland at all.
Is this really a flatpak issue? I've been dealing with this with Firefox periodically for many years, even before flatpak
I run flatpak firefox and kde wayland and have no such issue