Firefox + Realtime API (WebRTC): voice sessions drop deterministically on the user's second speech turn

Same problem here. Was working a few days ago. Now after a few seconds, 2-3 turns, the connection failed with a “WebRTC: ICE failed, add a STUN server and see about:webrtc for more details” error in firefox console. In Chrome everything is working fine, Firefox has also worked in the past. Tested in different networks and OS.