Hi, I'm sorry to hear that! I did some research (I'm a fellow user, not associated with Firefox) and this is what I found: 1) Third-Party Cleanup Tools: CCleaner, BleachBit, or similar system cleaners may delete Firefox profile data if misconfigured. Check their settings for anything related to Firefox or browser history/data. 2) Antivirus or Security Software: Over-aggressive settings (e.g., from Avast, Bitdefender, etc.) can sometimes interfere with Firefox profiles.Check quarantine/logs in your AV tool for anything involving Firefox. 3) Malware or Browser Hijackers: These can delete or overwrite bookmark files. Run a full scan with Windows Defender, Malwarebytes, or a reputable antivirus. 4) Firefox Reset / Refresh: If you (or another app/script) triggered a Firefox Refresh, it moves old profile data to a folder on your desktop named: Old Firefox Data In the future I would suggest enabling Firefox Sync so bookmarks are stored in your Mozilla account! Hope this helps.