People, this is true innovation in the browser's world and it's going to ignite a little revolution in the way we are writing web pages. Let's all say a big bravo and thanks to Robert O'Callahan who implemented basic support for CSS3 columns in Gecko. Here is a screenshot of Composer editing a single DIV element split into two columns:

multi-columns in Gecko

roc, you rock! Guess what ? Nvu is going to support that soon, you can bet on it :-)