Firefox keeps backup of the bookmarks in the bookmarkbackups folder, so you should be able to restore a recent backup to restore this lost folder. *https://support.mozilla.org/en-US/kb/restore-bookmarks-from-backup-or-move-them The name of an automatically created JSON bookmarks backup in the bookmarkbackups folder includes a total item count (folders and separators included) and an hash value to prevent saving the same backup more than once. You also see this count in the Restore menu drop-down list. *bookmarks-YYYY-MM-DD_<item count>_<hash>.jsonlz4. Note that Firefox keeps a full undo stack of changes to bookmarks for the current session. So if you haven't closed Firefox, you can open the Bookmarks Manager (Library; Command+Shift+O) and use "Organize -> Undo" (Command+Z) until you see the deleted bookmarks reappear.