> - distro are usually slow to ship new updates
Depends on the distro. Some focus on stability (like debian), so that's intentional. Others focus on quick updates (like Arch) and they usually succeed. Either way, if there's a serious security issue, the packagers will be definitely be notified and ready to ship the update immediately after upstream, hopefully along with a push notification to their users to update ASAP.
> - when u update running Firefox under its feet using distro package manager, it won't like ... everything crashes.
I haven't had that happen in over a year - Firefox just says "please restart to keep using Firefox" on new tabs. And you're the one triggering the update, so it's the same as a manual install.
> - not distro ff applies update patch when it starts or shows yellow notification on right side to say update is ready ... much better UX.
Updating on startup is horrible UX - what if I'm on really slow wifi or have a weak computer? Now I have to wait multiple minutes for my browser to start. As for update notifications, most distros that provide GUIs for their package manager also provide update notifications that you can enable.
> - snap packages have uses, but I do not like sth Firefox as snap, unnecessary bloat.
So...don't use snap? Every distro I know packages Firefox using the native format, snap is just another option that you're free to ignore.