Matching Thunderbird fields to text file fields can be tricky. Using
this feature is a little like putting together a puzzle. Almost every
time you move a Thunderbird field it displaces a field in the text
file. The displaced field in the text file may bounce another field
that is correctly matched to a field in Thunderbird. You have to
be patient and take your time while doing this. You want import
the contact list correctly the first time that you do it. It's no fun
to have realized that the import did not work properly and that
you have to do it again or, even worse, that you have to
manually update your contact information.
Importing a contact list from a web mail application like Gmail
can be very daunting because Google's contacts file contains
many more fields than does Thunderbird's address book. You
can make this a little simpler by opening the Gmail export file in
a spreadsheet program, deleting the unwanted columns, and
saving the file in CSV format. The smaller file should be easier to
handle when importing into Thunderbird.
To export contacts from Thunderbird a text file for importing into
another application, open the Address Book go to the Tools menu and
Export. You will be prompted to specify a name for the output file
name and an export format. The three export formats are LDIF, CSV
(comma delimited text), and tab delimited text.