Mozilla does not offer Firefox email accounts. A Firefox Account is only for using certain optional services and you need to associate it with an existing email account you have with a different provider.

This article has more information on Firefox Accounts: Access Mozilla Services with a Firefox Account

If you need a new email account, there are a wide range of providers, many free (with advertising in your online inbox), with a range of privacy policies...

Mozilla only provides @mozilla.org email addresses to a select number of people who work for or with Mozilla.

Firefox is a web browser and not a email client as a web browser deals with email by way of a webmail or web based email.