Bookmark backup in Firefox!
If you go in the Bookmarks menu and click on "Organize Bookmarks...", you can restore bookmarks from a backup. Backups are done automatically every day. It is like a Time Machine for bookmarks. The advantage is that you can restore in case you accidentally delete a bookmark that you wanted to keep. To access the backups, click on the star icon that is in the toolbar and choose "Restore". The latest backups will be displayed.