In order to "import" backups, you MUST have a VALID BACKUP.
FF does not automatically make a backup, YOU must do that every once and a while..
So once and a while you simply go to HISTORY, SHOW ALL HISTORY, and select BACKUP AN IMPORT YOUR BOOKMARKS.
Otherwise, failure on your part to make a backup and suffer the consequences.
Now, you can sort of recreate some of your bookmarks by sifting through the HISTORY of your surfing..
Gonna be a long time consuming process..
Alternately, if you have bookmarks set in your IE, you can use that as a starting point to import into FF.
Now, what lesson did we "learn" today?
Backup, backup, BACKUP.
Hint, backup your OS also, a good backup of it WILL save your bacon some day..