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.

Flatpak Firefox and Chromium are very different. Note that Flatpak Firefox starts normally fast for me.

Use the native version, it is one of the best maintained software and has access to “user namespaces” for isolation.

Now search on the internet what that is XD

The only “Firefox” not presenting this start issue for me is Floorp but it’s proprietary.