A partial implementation of WebRTC will only come to Firefox’s experimental nightly builds later this quarter, so it will be a while before you will be able to use these features yourself (though there are, of course, already plenty of Flash-based video chat tools out there).
Just like HTML5, the WebRTC standard is still under heavy development. It’s worth noting, though, that all the major browser vendors (Mozilla, Microsoft, Google and Opera) have voiced support for this technology and the Chrome Dev channel, for example, already offers a WebRTC API.
For now, this is obviously just a demo and it’s not clear if Mozilla will actually bake this feature directly into Firefox. Given that Mozilla has shown interest in adding all the underlying technologies to the browser, though, it wouldn’t come as a major surprise if it would at least offer its own video chat feature as part of the Persona initiative.