4
depends, if you have your center column set at width:100% it may not.
BTW you are missing a closing bracket on one of your style declarations, that may be contributing to the problem.
*Edit* In firefox it is indeed different. I also noticed you used the wrong method of "commenting out" things in your CSS. You can't use HTML or PHP comment tags, the correct way is to use /* comment here*/ tags. Firefox probably doesn't like that either.