The Problem:
Note: This only applies to XHTML 1.0 Strict Doctypes and Mozilla.
I make this type of layout all the time!  Two fixed width columns on either side of a fluid column.  Recently I had to put a list of article teasers into the center (fluid) column.  No problem, I marked up an unordered list, floated [...]

clearfix, CSS, FF, FireFox, HTML, UL, Unordered List Hide