Mozilla's Opus codec

Opus audio codec is supported since Firefox 15, and is being introduced as the codec which provides the highest quality and lowest latency with the same bitrate as of today.

Google proposed this codec as the standard audio codec for WebRTC, and Chrome does support it but with '--enable-opus-playback' parameter.
http://www.ietf.org/mail-archive/web/rtcweb/current/msg04953.html
http://code.google.com/p/chromium/issues/detail?id=104241