Firefox is one of the few exceptions I suggest always use native version

If it is due to an inefficiency of Firefox it seems strange to me that no fork has solved the problem, other browsers like Brave work perfectly.

Not only because of performance issues, but also because it’s clunky sometimes. For example, I cannot use KeePassXC Browser extension on Flatpak Firefox cause this implementation is borked. However in native version works flawlessly

The extension is probably not broken because of Firefox but because Flatpak’s sandboxing prevents it from talking to KeePassXC.