The homepage looks fine. The problem seems limited to the About and Portfolio pages.
I had a look and, well i’ve been scratching my head for a while actually. It turns out you have a few syntax errors in your css – it’s always worth running it by the validator and fixing those just incase it’s screwing with IE / Firefox.
That’s by the by. You are actually referencing two different style sheets
http://graemepirie.com/wp-content/theme … /style.css (13622 bytes) in homepage
http://graemepirie.com/new/wp-content/t … /style.css (13503 bytes) in about, etc…
So subtle that like I say it took me some time to spot it myself.
I suggest you use <?php bloginfo(‘stylesheet_url’); ?> in your template to correct this issue :-)