I've never tried it, but a google search brought this up
http://linux.softpedia.com/get/Commu...in-33014.shtml
It says its for Thunderbird 2.0.0.x, but it may still work in a 3.x version. If not, you could install an old thunderbird version to import into, then save in Thunderbird's format from there to use in your up to date Thunderbird.
Edit: Also, welcome to LinuxQuestions!