> the web is not the browser
Actually yes, the web is the browser, or more correctly the browser is your interface to the web. HTTP/HTTPS is the web, everything else is the Internet. Mozilla is focusing on providing a web experience, a SMTP client is not the web experience and they no longer wish to expend resources on it.
https://groups.google.com/forum/#!msg/mozilla.governance/kAy...
Take Andrew Sutherlands email for example, that directly, out in the open, discusses the very points you raise:
https://groups.google.com/d/msg/mozilla.governance/kAyVlhfEc...
"The problem with Thunderbird is not that it is a mail user agent or that user agency in messaging is unimportant. The problem is that Thunderbird has had a serious technical debt problem since the day its code-base transitioned from Netscape. Its low-level integration with Gecko has been a maintenance burden for Thunderbird developers and non-Thunderbird developers alike.
The Mozilla Foundation and Mozilla Corporation put serious financial resources into trying to address both of these problems with the creation of Mozilla Messaging. The idea, as I understand it, was to attempt to alleviate the burden on Firefox development by separating Thunderbird development while simultaneously providing Thunderbird with people and resources to attempt to address this technical debt."
"An important question that falls out from all of this is and your original question is: which is more important? Mail user agency or Thunderbird the product, especially if there are serious opportunity costs related to Thunderbird?
Within the funded efforts of the Mozilla Corporation[2], mail user agency has not been abandoned and continues to be advanced as part of an open development process."
Switching search engines from Google to Yahoo instead of giving users a choice at install is not building a better web for users.