The navigation bar on my site http://hungryathome.net doesn't center properly on Firefox and IE8 Standards mode. It centers properly in IE7 Compatability mode and in Chrome.
What's odd is that setting a Margin on the div (id="navlinks") to 4px or more will make it center properly. Any less will result in it being slightly off-center. I changed the values back and forth in Firebug and it's confusing the heck out of me. Any explanation for why that's happening?
Aha, looking at Firebug using their awesome controls which put the blue color over the elements, your header image is actually hanging down about 3 or 4 pixels over your nav bar, which is causing it to move the nav over and actually make it smaller, so it is centering it "properly". Try making your header a few pixels taller until it snaps into position correctly.
EDIT: Or apply a border: 0 style to that image so it doesn't add the border around it, might be a better solution...