More than likely it was a failed package transition that failed. You were running one version, an update triggered, something went wrong, and your data folders got orphaned. You can try running a repair on the package, but they usually fail the same way.
I don’t have any advice for this exact problem but if it’s any consolation Firefox has randomly gotten offended at my video drivers and bricked my build. Multiple times. I use Librewolf when I can now.
That is hilarious though, sending frustrated IT vibes your way in both empathy and hopes it’ll help you reach the critical mass of superstition for the problem to fix itself before you have to threaten to take a hammer to it.
As someone formerly involved in security at the enterprise OS development scope, I consider one less Flatpak to be an improvement in security and consistency.
Firefox is still extremely messy on Linux. It’s split between multiple platform types (flatpak, deb, snap) and I’ve seen multiple parts start to branch off on their own due to some fault. It’s really weird. Can’t even describe it. Why can’t they just do things simply.