That is not really true.
Yes, our Firefox support has not been great, but we are working on making it better: https://github.com/jitsi/jitsi-meet/issues/4758
> Desktop sharing? Chrome plugin.
This was a browser limiation, which is no longer needed since about 2 years ago.
> Desktop client? Chromium/Electron.
You need to ue it! Use the browser, or the mobile apps.