Yes we agree, email has become an identity used to sign up for things (usually through OpenID) and a notification center. But few are keeping in touch with their friends through email, this is not 1998 "You got mail" with Tom Hanks and Meg Ryan anymore.

Notice that as an ID and in the last 10 years it had the compete again with the phone number that has become mandatory to sign up to a lot of services like WhatsApp, Twitter, Clubhouse, Tinder, etc. to limit fake accounts.

Also digital government ID are now being rolled out so email will become less and less central for work, school applications and "real world" services.

So yes I am curious why Mozilla believe email will save them, but I keep an open mind they might have an idea.