Expanding div's

Hi there,

I’m working on a new website for the company I work for. I made this new site completely in xhtml with div’s and css.

It’s almost done and working but there is one little pain in the *** problem I can’t figure out.
There are three div’s next to each other, the middle div is filled with content from a database and will scale in lenght when more content will be filled in.

The freaking problem is that the left and right div don’t grow with the middle div!

i tried the solution explained in this toppic http://www.kirupa.com/forum/showthread.php?t=195006

But that only fixes the problem in IE not in Mozilla Firefox, Someone who can help me fix this irritating little bastard???

Tnx in advance