I read about the
Google Browser Sync extension a while ago, but I gave it a try yesterday, as I recently setup a dual-boot with Ubuntu. Basically, the extension allows you to keep two different Firefox browsers in sync. You can sync cookies, bookmarks, saved passwords, history, and even your active tabs. The extension stores these on your Google account online and applies changes when you load your next browser.
I use it to sync my cookies and bookmarks between Ubuntu and XP. I have grown to love it now.
I just wanted to point out a useful tool for us Firefox users.