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…
http://www.joelonsoftware.com/articles/fog0000000069.html
Joel was right and wrong.. Firefox was a huge success (or at least in my mind it was) but some might say the Netscape company was trashed during the process (I don't know if I agree).
Starting over isn't always a bad thing but I agree that is also highly overrated.