Not a big issue, by-any-means, login with email has an odd case-sensitivity issue.
Changing the case of your username (before the @) behaves normally, asking for a password and then MFA:
username@mozilla.com
Username@mozilla.com
userName@mozilla.com
Changing the case of your domain (after the @) behaves differently, asking to send an email:
username@Mozilla.com
username@mOzilla.com
username@mozilla.Com
Just figured you guys would like to be aware.