If you use Firefox on more than one computer, you'll want Foxmarks. Install Foxmarks on each computer, and it works silently in the background to keep your bookmarks and (optionally) passwords synchronized. Foxmarks also keeps your data backed up and safe from computer failures. If you're away from your computer, Foxmarks allows you to access your bookmarks online by logging into my.foxmarks.com.

Try it out: https://addons.mozilla.org/en-US/firefox/addon/2410