Their devs are probably trying to make sure it runs in Firefox but they haven't added it to the official QA process, just like they haven't added languages other than English either. And they don't want Firefox users complaining about bugs that might be there yet.
If this were a full release then sure I'd complain too. But this is just a beta. Maybe releasing betas before they have full compatibility and internationalization is good, rather than "miserable"?
Sorry but have you ever developed software before? I’m sure you have. You’re just refusing to draw from your professional expertise. Rather, you’re drawing from the “uninformed member of the Apple hater peanut gallery” part of your brain.
You wouldn’t have given this a second of extra thought if it wasn’t done by a company you’ve obviously long-since decided that you hate for cultural reasons.
It being in "beta" is a perfect reason to excuse bugs if it doesn't work in Firefox. But, they went out of their way to build in a system to say "go away" if you're not using Chrome.
That’s not what beta means. Why would I put something out there for beta testing externally that I haven’t done any internally testing for? Any feedback would just generate noise and issues that I already know about
https://beta.maps.apple.com/asd as an example.