See https://https://developer.mozilla.org/en/HTML/HTML5

Thanks for your reply, but I'm not a developer, and I don't see anything on Linux here. Can you verify that HTML 5 will be supported on Linux?

Support for HTML5 is the same on all platform.
If a feature is mentioned as being supported then it should work on Linux.

Yes, HTML5 is supported on Linux, Mac, Windows, Android, every platform that Firefox 4 or later is supported (The newest version of Firefox 10 and above do add new capabilities to the HTML5 support). The link cor-el gave simply describes what parts of HTML5 are supported.