You can restore the bookmarks from a recent automatically created backup in the bookmarkbackups folder. *https://support.mozilla.org/en-US/kb/recover-lost-or-missing-bookmarks *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.