Mozilla the makers of the Firefox web browsers and other products does not provide a email service to the general public. They may manually provide a @mozilla.org email address to people who work for Mozilla in a capacity that warrants having one. The person has to give up their mozilla.org email address when they leave. The Thunderbird community however is looking to provide a paid email service https://www.tb.pro/ that you can join a waitlist for. What "Mozilla Accounts" are used for besides this support.mozilla.org site. https://support.mozilla.org/en-US/kb/access-mozilla-services-firefox-account#w_what-services-can-i-use-with-a-mozilla-account