Yes even when I log into Outlook M365 from Firefox on Linux it's constantly kicking me out. Every time I get back to my computer it gives me this passive agressive "Please hold on while we're signing you out..." when I never asked to sign out. Grrrr.

I also notice it works way better in firefox if you set the user agent to Edge on windows. Some features which are broken in firefox suddenly work totally fine. Which reinforces my belief that they are simply doing this to bully people into using Edge.