There’s a Facebook app and messenger app in the repos. Think they’re in manjaro repos but definitely in the aur if not. I use caprine for Facebook messenger, more features
Probably not a Firefox problem. It’s the site not testing on Firefox and/or not supporting Firefox.
This scenario happens when Firefox user share drops below a value worth supporting. Risk is that Google/Chrome push their own agenda for web technologies and decrease interoperability and accepted standards.
It seems trivial, but the difference between a few pixels matters. Prepared graphics can make it harder for users to get a message, but they can also make it meaningless.