It's not standardised yet but there's a [spec](https://github.com/MozVR/webvr-spec) and implementation in [Firefox Nightly](https://nightly.mozilla.org/) (and [Firefox Dev Edition](https://www.mozilla.org/en-US/firefox/developer/) and soon in Firefox stable) and [experimental builds of Chromium](https://drive.google.com/folderview?id=0BzudLt22BqGRbW9WTHMtOWMzNjQ&usp=sharing#list).