These instructions should work for any version of Thunderbird, Macintosh and Windows.
Export your Thunderbird Address Book
- Start Thunderbird.
- Choose Tools > Address Book.
- Under Address Books on the left, select Personal Address Book.
- Choose Tools > Export.
- In the Save as type box choose Comma Separated (.csv file extension).
- Enter any file name and location to save (you'll need to remember this when you are ready to import your address book into your Gmail account.
- Click Save.
Import your Thunderbird Address Book into Gmail
- Login to your Gmail account.
- Open your Contacts.
- From the More Actions pull-down choose Import.
- Click the Browse button and locate the file your exported from Thunderbird.
- If you want these contacts to be in a new or existing group, check the box next to Also add these contacts to and make the appropriate selection.
- Click on the Import button.
- When the import is complete, click the OK button.
NOTE: this action does not synchronize your Thunderbird Address Book and your Gmail Contacts. It is a one-time procedure to get a copy of your Thunderbird Address Book into Gmail. If you are interested in sync solutions, visit the Mozilla Thunderbird Add-ons page (choose Tools > Add-ons from the main Thunderbird menu). There is a third-party add-on called Zindus that may work for you.