This is actually in the release notes for Firefox 118 here (https://www.mozilla.org/en-US/firefox/118.0/releasenotes/), but it also works on Firefox 115+ (as is mentioned in the bugzilla page).

Things that are still missing for me:

• being able to send 1080p video. I have a 1080p 30fps webcam that can only send 1080p video when using Google Meet in chrome. On Firefox, only 720p is available.
• support for call control devices. I have fancy headphones that can e.g. unmute you in Meet when you lower the microphone, but registering such a device with Meet is only available in chrome. See https://support.google.com/meet/answer/12562325?hl=en