For what do you need to restore Firefox bookmark? Maybe you want to restore it when you want to reinstall your Firefox. Maybe because you accidentally delete it. If you just have a few bookmarks surely it will not be a problem for you, but how if you have many bookmark sites? It will take your time to remember some of them and surely will impact your job.
Firefox provides automatic backup Firefox bookmark for last 11 day and manual backup. To backup manually just click Firefox Bookmark button at top right Firefox menu bar and click Show All Bookmark menu or just with press CTRL+Shif+B from your keyboard as shortcut to open bookmark manager and just click Import and Backup then click Backup to backup your Firefox bookmark into your computer as JSON file then save it.
When you have a problem with bookmark you can easily restore it. How to restore Firefox bookmark with automatic is easy from Bookmark manager. Click Restore and choose one of available backup. If you want to use your backup JSON file just click Choose File then you need to locate your JSON backup file that you have saved previously with manual backup.Next it will provide notification that your backup will replace all your current bookmark and click Ok.
Maybe you have more than one computer and you want to have same bookmark so you can easily use your backup file to restore in every computer you have. Actually there is another option in Firefox to manage bookmark with import and export html file as backup and restore.
I hope this tutorial will make you more comfortable with computer and internet.