The link below lists all the default fields used in the 'Address Book'. http://kb.mozillazine.org/Import_address_list_from_text_file

When importing you need to map the appropriate field names in Outlook to those in Thunderbird by moving them up or down.

Sometimes it may be easier to export outlook address book as .csv file, alter column headers as required and then import.

Thank you for that link -- it was most helpful. By inspecting the .csv, it appears that the Thunderbird import tool displays the first 37 fields of the .csv as choices to Move Up/Down to align with the 37 Thunderbird fields. I would assume that if I want fields from the .csv that are not in the first 37, I will need to rearrange the columns in the .csv so that they are in the first 37. Is that correct?

Yes. Whilst rearranging in .csv, it might be worth while altering the column header name(s) so it is the same as one in Thunderbird, as this would help when using Move Up/Down to align.

If you want to keep an original copy of the Outlook csv, make a copy and use that one to make alterations and import. You can delete any columns not required knowing you still have the original.

Thank you again for your suggestions. I was able to import my Outlook contacts into Thunderbird with the fields properly aligned.