Bookmarks LinkChecker
Detects updated, redirected and broken links in bookmarks list by adding icons within the drop-down bookmarks menu.
https://addons.mozilla.org/firefox/1647

Alert Bookmarks
Alert Internet Tools Web Site has tools for Webmasters and Web designers. Our award-winning software is tailor made to increase productivity with a short learning curve. Download free trial versions!!
http://www.alertbookmarks.com/

SAB Bookmarks Converter
Bookmarks Convert will convert your Internet Explorer bookmarks to Netscape bookmarks and your Netscape bookmarks to Internet Explorer bookmarks.
http://www.saberman.com/SABBC/

Bookmarks Synchronizer
Bookmarks Synchronizer is a Mozilla Firefox extension that allows to synchronize bookmarks via an FTP server.
https://addons.mozilla.org/firefox/2367/

Online Bookmarks
_your description goes here_
http://www.online-bookmarks.com/

del.icio.us
Keep, share, and discover the best of the Web using Delicious, the world's leading social bookmarking service.
http://del.icio.us/

Yahoo! Bookmarks
Allows users to import bookmarks and organize them into folders. Also offers a toolbar to add into the browser.
http://bookmarks.yahoo.com

Bookie
An experimental application which keeps all your bookmarks on a central server so that you can access bookmarks from anywhere on the web, using a variety of clients.
http://bookie.mozdev.org/

Herbridg's Bookmarks
This collection of ODP bookmarks indicates Fritz's personal interests.
http://www.dmoz.org/Bookmarks/H/herbridg/

Foxmarks Bookmark Synchronizer
Foxmarks is a free add-on for your Firefox browser that syncs and backs up your bookmarks and passwords across multiple computers and more.
http://www.foxmarks.com/