If you haven't closed Firefox yet then see if you can use "Organize > Undo" in the bookmarks manager (Bookmarks > Show All Bookmarks) to undo this action and restore the bookmark(s). The Organize button is the first of the three buttons next to the Back and Forward buttons on the toolbar in the Library (Bookmarks Manager). If this didn't work then you can restore the bookmarks from a JSON backup in the bookmarkbackups folder. *Bookmarks > Show All Bookmarks > Import & Backup > Restore This will replace all current bookmarks and you lose bookmarks that were added since that backup was created. See: *https://support.mozilla.org/kb/restore-bookmarks-from-backup-or-move-them *http://kb.mozillazine.org/Backing_up_and_restoring_bookmarks_-_Firefox