How to match height of floating sibling divs

Question

I have the following situation: http://jsfiddle.net/F3SqM/2/

I have two columns, I only know of the height of columnB. Both columns are floating, and I want columnA to m

Answer 1

Quickest fix would be to use display:table-cell instead of floating:

http://jsfiddle.net/F3SqM/1/

However, this will only work in IE8+...