I just figured out how to get this site with all of its HTML5 goodness to display properly* in IE < 9 and FF < 4.  It seems that in browsers that support the new elements, they set them to display:block, but in browsers that don’t support them – where Modernizr adds them as a shiv – this property is not set, so must be set manually.

So, without further ado, just add this to the top of your stylesheet:

article, aside, details, figcaption, figure, footer, header, hgroup, menu, nav, section {

* properly = better. Obviously not “properly” since these browsers still don’t support the CSS3 goodness in use, but at least it doesn’t look like a pile of gecko poo now :)