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.
the only reason to use flatpaks is if your system doesnt come with a good package manager and repositories (pacman+aur, nix, etc), and dont want to build from source.
snaps, on the other hand, should be avoided at all costs imo.
Tied to proprieatry backend, snap store looks like ass and runs like one, spawns loop devices that mess up the /mnt folder, tied to fake .deb packages that install snaps instead. Basically, a lot of proprieatry nonsense that St. Ignucius frowns upon.