links not working in firefox

hey /prog/,
I have a problem: my site www.matthaspictures.com dosent work in firefox. well, everything works except for the links in the tabs. they turn into plain old text and i dont know why. it works perfectly in IE, but has the same problem in safari.

I didnt use a page generator of any kind, hand coded the whole thing from scratch. any idea whats going on? thanks so much!

i was lookin online and i read that it might be the z-index of my css div's. all the tabs that arent active are -100 in the z-index. would that affect my ability to click on links?