This is something one doesn't do use another computer and those data will wipe your previous data on all other synced devices. So unless you can find your jason4 backup on your own computer his data will now replace all your synced device data. What you should've done was create your own user account and that will prevent the wrong sync data from wiping the other account data sync information. https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile https://support.mozilla.org/en-US/products/firefox/sync-and-save https://support.mozilla.org/en-US/questions/1289446 https://support.mozilla.org/en-US/questions/1292341 https://support.mozilla.org/en-US/kb/ive-lost-my-firefox-sync-account-information https://support.mozilla.org/en-US/questions/1292900 What you need to do is remove all synced device so the backup can be found and restored. If you don't do this any chance to find or restore is lost the more sync you leave your computer with the login.