(X)HTML5 and other semantic elements not displaying correctly.?

I’ve heard that Firefox 3.5 (and Chrome/Safari to some extent) support HTML 5, but my test XHTML 5 page does not display properly.
XHTML 5 page is at: http://stuff.adammw.homeip.net/other/example.xhtml

I expected it to produce a result similar to: http://stuff.adammw.homeip.net/other/refrendering.html but it doesn’t.

Any answers or ‘css hacks’ to get modern browsers to display (specifically headers) correctly?
Thanks.
Thanks for your input, but I must admit I find it very strange. Out of the new features for HTML5, video and audio elements sound very hard to implement but they are, and yet something seemily simple such as these nested headings is taking so long.

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