See: *https://support.mozilla.org/en-US/kb/secure-firefox-account-two-step-authentication *https://support.mozilla.org/en-US/kb/how-do-i-know-status-my-sync When you enable 2FA for the Firefox account then you get a QR code that you need to scan with an Authenticator app that generates a 6-digit code that you need to enter to confirm that 2FA is working. You can generate and backup recovery codes that you can use instead of the 6-digit 2FA.