1) Launch Mozilla Firefox
2)Go to Bookmarks tab and click on Organize Bookmarks…
3) When Libary appear click on Backup under Import and Backup tab.
4) Save you backup. The file will contain all your bookmarks and will be an . JSON file.
5)When you need to restore your backup navigate to Import and Backup-> Restore -> Choose File… Choose your backup file saved as .json and your bookmarks will be restored.