If you have several computers, Foxmarks is excellent for syncing your FireFox bookmarks between them.
If you have only one, you can use it for backing up your bookmarks in case of a crash, corrupted bookmarks file, or disasters. And you can even share your bookmarks with friends.
Don’t trust them online? Well, you can have it use your personal server for syncing. Or worried about personal bookmarks at work? Just change the “profile.”
Download FireFox here: