I’m guessing you don’t work in corporate environment or no longer work from home.
There are times when video is expected to be on, but you don’t want to show your room to everyone.
Having said that I can’t think of firefox being able to stream video yet not being able to do this, so likely it is Google’s way to make its competitor look subpar. Probably can be fixed by spoofing user agent. Ironically the most recent change in Chrome will make this very difficult in the future.
It is privacy. I don’t have mess, just don’t feel like sharing inside of my house with strangers. Maybe I’m working in weird company, but I noticed that vast majority of coworkers either have camera off, blurs the background or sets up a fake one.