Last time this came up, just spoofing the Firefox user agent to Chrome made it work perfectly. Maybe they block it because they haven’t tested it on Firefox yet, but it works as well as it does in Chrome.
And if they haven’t had the time to validate it in Firefox yet, that is a conscious choice by MS to not dedicate time specifically to validating in Firefox and treating it as a second-class web browser.
Honestly just left it. Debating on putting carpet in the room where it’s pretty bad. But decided if I couldn’t do it well myself I’d just wait until I was ready to fork over money to have it done correctly.