Foxmarks is a Firefox plug-in that backups/synchronizes your Firefox bookmarks and make them available online at the website. If you reinstall your OS and Firefox, you never have to worry about losing your bookmarks. Just install the plug-in and type in your user name and password; all your bookmarks will be restored, along with their keywords intact. When you go out and are using a public computer, you can still access your Firefox bookmarks online at the FoxMarks website.

You can also backup your bookmarks using Google Browser Sync. But, Google Browser Sync synchronizes more than just bookmarks and it's found to be slow on first use (restoring back your browser settings and bookmarks). And Google Browser Sync doesn't let you access your bookmarks online. If you want to, you'll have to use a different service, Google Bookmarks, and you need to have added your bookmark to it when you bookmark a page to your Firefox. Google Bookmarks uses Labels instead of Folders and it doesn't, until now, support sub-labels. So, when you access your bookmarks online, they can be pretty unorganized, while on FoxMarks, everything is organized into folders and sub-folders just as you have created them in your Firefox bookmark toolbar.
Until then...
Justin
Technorati tag => FoxMarks