Unlike the original parent post I don't think this announcement anything to do with XUL. Thunderbird just doesn't have the userbase Mozilla expects it to at this point because, surprise, the people who want an email client are a small subset of the people who want a web browser.
<rant>
This is lost in a sea of replies now but I'm sure pissed off Mozilla is completely losing their root mantra of fighting for the free web. Persona, Thunderbird, two critical components of a "free web": free global authentication, free email client. I'm sure next mozfest the same suits as every year will talk about how they're so proud of "keeping the web open". What a crock of crap. Firefox isn't even that good of a browser anymore.
It is easy to forget that freedom and creativity are not a numbers game. There are benefits to a majority when a minority is free to create. An argument could be made that the majority consumption patterns are made possible by the minority creator patterns, hence it makes economic sense to fund the minority out of majority profits.
This is one of the reasons why iPads have stalled - pro developers can't make money, for well documented reasons. The web equivalent will be the starving of open communication, thought and creativity, leading to homogeneous noise as a poor substitute for ground-breaking content.
I don't see why it couldn't, they are doing it for FireFox. On the other hand Mozilla has been on the path to retire Thunderbird for some time, this is just the next step.
Mostly I think it is an effort vs reward thing. Thunderbird doesn't have the user base and doesn't have a revenue stream the way fire fox sells the search box. I wonder if anyone over there has thought about cleaning it up and selling it as a white label email client.
<rant>
This is lost in a sea of replies now but I'm sure pissed off Mozilla is completely losing their root mantra of fighting for the free web. Persona, Thunderbird, two critical components of a "free web": free global authentication, free email client. I'm sure next mozfest the same suits as every year will talk about how they're so proud of "keeping the web open". What a crock of crap. Firefox isn't even that good of a browser anymore.
</rant>