Arclite theme issue with Firefox 9 and IE 8

It seems that the Arclite theme does not work properly with Firefox 9 and IE 8. My header has changed color and my main navigation links do not look like they do in earlier versions of both browsers. I am considering changing my theme but first wanted to know if anybody knows of a fix for this because I like the arclite theme and if I change it to another theme I will have to go through over 150 posts to make sure all the images are in the right places etc.

Hoping somebody has a tip or an idea for me 🙂