As of November 2013, both Google Chrome (version 28 and above) and Firefox (version 23 and above) support WebRTC. Chrome v29 on Android is also supported.
However, Twilio Client only supports WebRTC on Chrome at this time. Chrome on Android is not supported by the Twilio Client. Instead, you can use Twilio’s SDKs to write native Android and iOS apps. If your browser does not support WebRTC, by default, Twilio will fall back to Flash.
Other browsers are investigating support for WebRTC and may release WebRTC capable versions in the future. Please refer to this link for the most up-to-date information about browser WebRTC support.