You can restore a bookmark backup. https://support.mozilla.org/en-US/kb/restore-bookmarks-from-backup-or-move-them

If you have accidentally removed bookmarks then use "Organize > Undo" in the bookmarks manager (Bookmarks > Show All Bookmarks) to get them back.<br /> 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).<br /> That only works if you haven't closed Firefox.<br /> If it didn't work then you can restore the bookmarks from a JSON backup.<br /> This will replace all current bookmarks and you lose bookmarks that were added since that backup was created. See: * http://kb.mozillazine.org/Backing_up_and_restoring_bookmarks_-_Firefox