You can restore the latest backup prior to the deletion. Backups are in a folder bookmarkbackups in your profile.

You can restore a backup using Firefox. ctl+shft+o gets you the Library. At the top select Import and Backup > Restore : select the backup you want to restore.

As long as you are in the Library window, you also can try

Organize > Undo

I don't know how long that is available.