FireFox compatable drop-down menu?

Question

Hi. I'm working on my first 'professional' web-design project (when I say professional, I mean I've been offered money for it) and I'be hit a little block in the road. I've got a great layout and design for the site... my customer and I are quite happy with how its turning out. There's just one problem... the drop down menu won't work in Firefox. It looks great in IE7, but in FF it looks terrible. Can anyone tell me how to fix this. Here's the HTML that I am using for each cell (5 cells in total):

Link

Also using: