You can export your bookmarks manually by following these instructions.
If you plan to use Google Chrome or Internet Explorer you can import your Firefox bookmarks directly from within these browsers, See these instructions:
Open Firefox and click Show All Bookmarks
Select Import and Backup, then Export Bookmarks to HTML.
Choose a location to save the file to, the desktop is fine because we will just import this same file into either Internet Explorer or Chrome.
You have successfully made a backup of your bookmarks. Now you can either move this file to a safe place to use it as a backup or you can import this file into another brower to have all your sites available.