Hello, When Mozilla detects that your credentials may have been compromised, often through data breaches found on the web, it proactively locks the account. This is a security measure designed to protect your sensitive information, such as stored logins and synced data from being further compromised. To unlock the account, you must reset your password. A password reset is required because it ensures that no data is synced to a device that may be controlled by an unauthorized person. Please see [[Reset your Mozilla account password to protect your credentials]] for reference. Please see [[How to change or reset your Mozilla account password]] on how to reset your password and keep your encrypted data (you'll need a recovery key for that). Resetting the password without a recovery key deletes synced encrypted data (bookmarks, history, tabs, passwords etc.) from Mozilla’s servers, but local copies on your device remain and can be re-synced upon login (that is also covered in the article). Please also note that Firefox Sync is '''not''' designed as a back up service. Sync takes a copy of the data you wish to include and transfers it to a second device (typically a mobile device such as a tablet or a telephone) running a copy of Firefox. The storage in between all attached devices is both temporary and fragile and is not stable enough to be (and is not designed as) a reliable backup service.