1) First in the upper left hand corner click on
2) Click on Bookmarks > Show All Bookmarks
3) Click on Import and Backup > Restore > Choose File
4) Navigate to your H: drive and locate the backup file. There should be a .json file called "bookmarks" followed by the date your bookmarks were backed up. Select the file and click "Open".
5) Finally click "ok"
Your bookmarks should now be restored in Firefox.