You're missing a close tag somewhere, I'm sure of it. The thing is, Firefox has a code correction feature which will attempt to fix code when it's wrong. Which is why testing pages in Firefox is a no-no for real web developers

You never know when firefox will approve bad code.
Validate your page code
http://validator.w3.org/
See where it complains about missing tags and you should be able to solve the problem. Also, get
Opera, it's far better at showing you code problems than Firefox.