"Firefox Hello lets you make free video and voice calls directly from the browser. All you need are a microphone, a webcam (optional), and the latest version of Firefox to call friends who are on WebRTC-supported browsers like Firefox, Chrome, or Opera."
This is similar in concept to Jitsi Meet (https://meet.jit.si/) tested earlier but now integrated with Firefox so its even easier. Apparently, Mozilla is using OpenTok (https://tokbox.com/), a WebRTC platform for adding live video, voice, and messaging to websites and mobile apps.