Tools Import Address Books Programs List is blank

In Thunderbird Portable 2.0.0.6, when I access the following menu sequence, Tools / Import / Address Books / my only result is a dialog box with no options. No programs are listed in the "Select the program from which you would like to import" list and the only remaining option is to cancel or go back.

I have properly formatted CSVs and LDIF address books waiting in the wings but have no visible way to import the data.

The export function works correctly, just not the reverse! In fact, all Import options (Address Book, Mail, Settings) are returning empty "Select the program from which you would like to import" lists.

Any ideas?

~S