The decision to use a suite like mozilla vs standalones like Firefox+Thunderbird is a matter of preference.
The development of the mozilla suite is over, although it will be maintened if vulnerabilities appear, unlike Netscape, which has hit a brick wall.
And, there is Seamonkey on the horizon, for new developments, and, why now, Donzilla is already here.
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8) Gecko/20051205 Donzilla/1.0 (WML/1.3)
