This issue is about a problem on steamcommunity.com, not anywhere in the steam client itself. It's also unrelated to Linux. Apologies for being a bit off topic but this tracker still seemed like the best place to file a report.

Firefox has a list of compatibility overrides which you can see at about:compat. One of them is a User Agent override for steamcommunity.com because the voice chat there claims that Firefox is unsupported even though it very much works (at least nowadays, no idea how the situation was historically).

The root cause is a plain and simple whitelist in InitiateVoiceChat that only accepts Chrome or the Chromium-based version of Edge. (Originally figured out here).

Could you please drop this check or at least blacklist known broken browsers instead so that the override can be dropped from Firefox?

Tested with Firefox 107.0.1.

Related issues on the Firefox side:
https://bugzilla.mozilla.org/show_bug.cgi?id=1570108
https://github.com/webcompat/web-bugs/issues/34171

Steps for reproducing this issue:

(mostly copied from https://github.com/webcompat/web-bugs/issues/34171#issuecomment-507659362)

1. Navigate to about:compat in Firefox.
2. Click on the Disable button next to steamcommunity.com to disable Firefox' workaround. It's in the second row.
3. Navigate to https://steamcommunity.com/chat/
4. Click the "Manage friends list settings" gear icon.
5. Click "Voice" on the left.
6. Click on the "Start Microphone Test" button.