You can easily transfer your Thunderbird Address Book to Google Apps Mail Contact by creating a CSV (Comma Delimitated) file. But you will need to edit the CSV file in order for the migration to run smoothly.

Tips to remember when importing contacts

• You can import 3,000 contacts at a time.
• Non-ASCII or non-Latin characters may not be accepted.
• Any information formatted as a group or distribution list won't transfer into your Google Apps Mail Contacts list.
• Importing information that matches the email address of an existing entry will replace the information in your Contacts list with the most recently uploaded information.