https://addons.mozilla.org/en-US/firefox/addon/2410
Basically its a firefox addon that allows you to keep your bookmarks synchronized. I tend to jump around between laptop and desktop throughout the day and nothing agitates me more then bookmarking something on my laptop and then not having it on my desktop.
With xmarks now anytime I bookmark a page all I have to do is go to the other machine, click synchronize, and now I have the bookmarked page and login.
Never been happier.