Good morning fellow CSS'rs!

I have a site that I'm close to finalization on. One problem I am encountering is that in FF - after choosing a page (say, About Us), the menu across the top does not do the 'hover/replace' as it should. Does anyone know a work/repair for this?
The link to the draft site is www.keenwebdesign.com/test/GLL/


Thanks!
Lynn Keen
www.keenwebdesign.com