Their post has some examples to try out and instructions on how to use the <video> element.
Some very experimental binary builds if you want to try things out:
Be aware that these are builds from a random point in the Mozilla CVS tree, with the Video patch applied. I don't guarantee they'll work for much more than demonstrating video support and it's very likely to contain bugs. That said, I run these builds often.
It's very cool to see video support using patent free formats running on more than one browser, with simple HTML that can be embedded by anyone. Thanks Opera!