Truthfully, Firefox is fairly easy to detect. Several facets of the API it uses makes for quick identification. For example, Firefox should be able to report its build ID. Also, it won't report specifics about the WebGL renderer you're using like the vendor and architecture.
The link you shared is great and really highlights something I was thinking about today regarding this subject. The more you harden and change things the more you stand out. You're also more likely to trigger bot detection when you alter specifics about your browser like the major version you're on. I've seen some extensions change the user agent to much older major versions like Firefox 60. That's a big red flag.
The user agent thing was bizarre, especially since it was also on Minecraft.net! I swapped to a generic Chrome on Windows agent and it instantly started working again and let me use the site as normal again.
Yes that is bizarre 😂
It's not clear to me if Microsoft is using their own anti-bot solution or a third party one, but it doesn't sound really successful with the way it's reacting.
Overall, I can't help but thinking the best route is to use the same thing as everyone else but roll your own VPN and change MAC addresses. Ideally, we would have some laws against all of this but I don't foresee that anytime soon.
I wish I could do more to help. I'm happy to answer questions you might have, though.