As soon as I installed this extension and rebooted, my Firefox changed. After being in tune with how Del.icio.us, Digg, Google, Slashdot, and all of the other sites display their news, this was definitely a different way of displaying a list of articles.
The MultiColumn extension takes a familiar web-site and formats the list into a multi-column display, similar to a newspaper format.
When I started working with the web in 1996 (WOW, 10 years?), I didn't always like the horizontal scroll bar on the bottom of web pages because I felt like I was missing something. Now, with this extension, I AM missing something so I need to move sideways to get the news. :-) Thats just my opinion, I could be wrong.
This is absolutely the extension you need when you have two or three monitors. If you don't have two or three monitors tied together, then pass on this extension.