Need CSS Help- Looks Fine in IE, Broken In Firefox

I know a bunch of you are really good at diagnosing problems in firefox concerning css, so I was hoping to get a try for help here.

The site in question is: http://www.arscompendium.com

The main page is fairly alright, there’s a problem with the margin of a couple of things, but in general- it’s not bad.

However, it’s the actual article pages inside the site where the “tables” break apart and collapse downwards. Is there something I’m missing or not using correctly in my css?

Thanks!

David