At the end of 2019, we announced an upcoming requirement for extension developers to enable two-factor authentication (2FA) for their Firefox Accounts, which are used to log into addons.mozilla.org (AMO). This requirement is intended to protect add-on developers and users from malicious actors if they somehow get a hold of your login credentials, and it will go into effect starting March 15, 2021.
If you are an extension developer and have not enabled 2FA by this date, you will be directed to your Firefox Account settings to turn it on the next time you log into AMO.
Instructions for enabling 2FA for your Firefox Account can be found on support.mozilla.org. Once you’ve finished the set-up process, be sure to download or print your recovery codes and keep them in a safe place. If you ever lose access to your 2FA devices and get locked out of your account, you will need to provide one of your recovery codes to regain access. Misplacing these codes can lead to permanent loss of access to your account and your add-ons on AMO. Mozilla cannot restore your account if you have lost access to it.
If you only upload using the AMO external API, you can continue using your API keys and you will not be asked to provide the second factor.
March 24, 2021 update: If your authenticator offers you an 8 character token, check its settings to see if it can provide a 6 character token. Firefox Accounts will not accept 8 character tokens.