With .Mac, Apple users have been able to sync their Safari bookmarks between multiple machines for a while now. But with this setup you are limited to using a Mac (obviously) and Safari.

Now there is a way to synchronize your Firefox bookmarks as well, and thanks to the cross-platform nature of Firefox, you can also synchronize your bookmarks across any OS platform that Firefox is available on. Bookmark something on your PC at work, and see it on your Mac when you get home.

It works by using your own FTP server to store an XML file which can then be parsed into your bookmarks list by Firefox.

Try Firefox Bookmarks Synchronizer

Note: If you are currently using Safari and would like to import your bookmarks to Firefox in order to take advantage of this plugin, you can use the Safari Bookmarks Exporter to send your Safari bookmarks to Firefox.