How to Backup your Firefox bookmarks
How to Backup Your Bookmarks Manually
From the Firefox menu bar go to Bookmarks Organize Bookmarks to bring up your bookmarks manager. Now you want to click the top button that says Import and Backup.
Next, select Backup. This will bring up a “Save As” box where you can save your bookmarks to any location. Make sure you leave the bookmark as a .json file too. Since Firefox 3, this is the type of file Firefox uses for backups. If you wish to export your bookmarks as an HTML file, go to Import and Backup Export HTML. That will give you the more traditional .html backup.