This is probably not recommended (maybe some things break, I haven't really tested it), but as a workaround I'm changing the browser's User Agent to Chrome with an addon (addons.mozilla.org/en-US/firefox/addon/user-agent-string-switcher/, but there are others. I like this one because I can change the User Agent only on specific sites that try to force me to use a different browsers).
This does nothing other than skip the website's compatibility check, so things may break, but after some light testing I've had no issues yet. I'm guessing the website is mostly compatible with Firefox, but the team hasn't had time to test it, so they're reticent to give us the go-ahead.
So yeah, I'll use the website on Firefox anyway. I know it might be risky, but I don't want to use Chrome, and I don't have (nor want) an Apple device, so Safari is out too.