More frequently than I care to admit, I seem to close FF instances which I don't want to close (such as my connection to Whatsapp). I then miss important replies or questions. Of course I can reach out to 'History' and try to find the closed Tab or Window... But that takes time.

I'd suggest adding/removing a 'protection' flag to a tab (eg. on right-clicking), so that, on trying to close the tab, or close the window containing the tab, I get a warning...