They want to kill XUL for Firefox so they can be all fancy HTML. So they have to kill Thunderbird, a XUL app. In a few years the all new HTML Firefox will come out. My bet is that it will suck. It will lack a TON of features that the existing Firefox has, but hey, it's all HTML! And you won't be able to stick on the old one, because within a week or two some critical security flaw will be discovered and eventually (l…
It happened before, with the transition from Mozilla Suite to Firefox. And let's be honest: XUL was just lipstick on the pig that is cross-platform development. HTML/CSS/JS are now fast enough to look like a slightly better pig, so here we go. Also, there's a generational shift underway. You and me could find crazy that people would openly choose to use IDEs built on HTML/CSS/JS, but that's what a lot of young folks…
From the same source, apparently the Mozilla Foundation does a lot of important work that the Mozilla Corporation can't/won't do but most of the development is done by the Mozilla Corporation currently (possibly due to not enough donations to the Foundation?).
I haven't really verified that, but thought it was worth pointing out.