> Those who have stored account login credentials in their favorite web browser will need to transfer these credentials to the new domain to continue accessing the account. We have integrated an automatic transfer of the stored credentials, which you simply need to click through: Please visit the old login page "mail.tutanota.com" and you will be prompted to migrate your credentials with a few simple clicks.

I didn't know that this was possible. It is a feature on browser's password managers? How it works?