It sounds like you had Sync enabled on that device when you cleared your passwords. Sync runs real-time and will send changes ''(both additions and deletions)'' thru to the Sync server immediately. Only bookmarks are automatically backed up, no other date like passwords are backed up. No way to retrieve that data once it is deleted; ''other than Operating System restore points, but Firefox data has to be specified before hand to be able to do that.'' Don't launch any other devices that are connected to that Sync account, or the "lost" data will be synced to those devices, too. Before opening Firefox on those devices change your password for your Firefox Account ''(Sync account)'' to reset your data on the Sync server. Then when you reconnect those other devices to your Sync account with the new Password your data will be sent to the Sync server from the first device that your reconnect.