really bizarre bug in my html - not focusing on nav links with tab key press / duplicating elements

Question

for reasons unknown my html is causing all browsers, except firefox and ie, to skip over the links in the nav element when using the tab key, doesn't focus on them at all. firefox does something equally bizarre but different, it doesn't skip the links, instead it duplicates the header link and places the h1 element out of the link within the header. and with ie it works spot on perfect... yeah i know... (woah!)

i've narrowed it down to being a problem within my html because it still happens with both javascript and css disabled. i haven't yet included a skip to main content link so it can't be that, i haven't used the tabindex attribute anywhere and it all validates perfectly fine.

here's the problem to see for yourselves - www.thisbengreenguy.com/creative.php

thanks for all your help in advance.

Answer 1

by converting it backwards from html 5 to xhtml strict i've got it looking right in firefox and working perfectly in opera as well as ie now. and with safari and chrome you have to use opt/alt + tab to focus. at least it looks as intended and is as close to completely accessible as i can get it.