Your comment is incredibly mean. Mozilla isn't competing with other "charities", they are competing with Google, Apple and Microsoft, the world's largest corporations.
The Mozilla Foundation might be a not-for-profit corporation, but they have the same constraints as normal businesses ... they have to secure reliable sources of funding, they have to preserve their resources, they have to be smart about investments, they have to pay salaries because people need to put food on the table and they have to plan further than the next quarter.
And given the incredible progress of Firefox, I for one am glad that they've cut unproductive projects.
The current Thunderbird is terrible. It has been a good browser, it might still have life in it, its developers might manage to evolve it and make it awesome, however I haven't been able to use it for more than a week and believe me, I tried doing so, repeatedly.
I was sad to hear that Mozilla is dropping it, but then again, when I heard this news, I was already long gone as a user. Nowadays I'm split between FastMail's and Gmail's web interfaces and MailMate (freron.com), all of which are so much better for my needs, the difference ain't even funny.
Seriously, a web interface and a desktop client made by one guy from Denmark are better than Thunderbird. Thunderbird basically needs a complete overhaul, but then ask its 25 million users how they feel about that, after all, if they wouldn't want the current Thunderbird, they would've switched to something else.