Is that Outlook the mail client, or outlook.com, this year's name for what has formerly been hotmail and live mail? If the former and it's in the same computer, Thunderbird should be able to import it. Otherwise, export your address book from outlook to a CSV file and then import this file into Thunderbird. It may be useful (if not also necessary!) to open the CSV file in your spreadsheet and trim out any spare columns - i.e. all the blank ones - before attempting to import it into Thunderbird.