Three of those browsers are just Chromium reskins, how are they supporting Chrome but not them?
This news doesn’t mean that it just will stop working in Firefox, it’s just that they don’t test and they don’t care.
It only happens when I try from Alpine Linux, so they might be testing for some musl-specific quirk and denying access just for not being the Firefox from a different distro.
"Unsupported" = "We don't test or develop with this browser in mind", not "This browser doesn't work." If that browser effectively mimics one that is supported, it usually works fine.