The ideal solution would be to use inline-block for the columns instead of floating. I think the browser support is pretty good if you follow (a) apply inline-block only to elements that are normally inline (eg span); and (b) add -moz-inline-box for Firefox.
Check your page in FF2 as well because I had a ton of problems when nesting certain elements (surprisingly, this is the one case where IE performs much better than FF).
