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.
Haven’t had this issue on Gnome, might be a KDE specific issue. I really don’t use KDE much except on my Steam Deck so I haven’t encountered it very often.