Importing mail and contact into thunderbird

[FX Fraipont]

This is a problem I have never been able to solve ans taht has plagued 
my various installs of different linux distributions.

How can I import into Thunderbird mail from previous  Thunderbird, 
Seamonkey or Mozilla  installations? The Import function only works for 
communicator 4, Outlook and something else. Merely copying the  inbox 
foolder in the right place into the new mozilla-thunderbird folder does 
not seem to work.

Thanks

Fx