This is the real message, to me.<p><pre><code>  Many inside of Mozilla, including an overwhelming majority of our
  leadership, feel the need to be laser-focused on activities like Firefox
  that can have an industry-wide impact.    With all due respect to
  Thunderbird and the Thunderbird community, we have been clear for years
  that we do not view Thunderbird as having this sort of potential.

  However, as I say, it’s clear to me today that continuing to live
  with these competing demands given our focus on industry impact is
  increasingly unstable.
</code></pre>
So, their stated goal is market dominance for Firefox, period. Nothing else really matters. Clearly they are failing at this goal, so they are focusing their resources on it and discarding anything else.