Contacts Import from Windows Live Mail
There should be some custom fields (more?) that could be also editable! Importing from WLM (csv file) leaves many fields in the "air" and the are lost!!! It is very sad to search all contacts to find what you have lost! Also sadder to search something that you knew you have (e-mail, phone) and that have been disappeared!
Wšykne wótegrona (2)
The Thunderbird address book has four custom fields -- they are visible on the 'other' tab when you open a contact. Also it's a good idea to edit your csv file manually before you import it into Thunderbird. If you prepare it so that it 'fits' the Thunderbird address book structure you minimise the risk of losing data.
The import of WLM or Outlook contacts is usually successful if you edit the WLM csv in a spreadsheet so that it has at most about 16 columns, and the column titles match the ones in the TB address book.