Firefox keeps automatically created backups in the bookmarkbackups folder, so normally you should be able to recover. *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. If you use Sync, best is to disconnect Sync temporarily during troubleshooting. There could be a problem with the <b>places.sqlite</b> and <b>favicons.sqlite</b> database files in the Firefox profile folder. *use the "Places Database" -> "Verify Integrity" button on the "Help -> More Troubleshooting Information" (about:support) page If errors are reported with "Verify Integrity", close and restart Firefox or reboot and retry.