Copy contact information from Thunderbird to your Yahoo! Address Book:

First, export your contact data from Thunderbird:

1. Open Mozilla Thunderbird version 1.0 or higher.
2. In the "Tools" menu, select "Address Book."
3. In the Address Book window, open the "Tools" menu and select "Export."
4. Select a location for the file you are about to create, and give it a name that you will remember. For "Save as type," select .ldif.
5. Click the "Save" button.

You should now have an .ldif file saved on your computer.

Next, import that file into your Yahoo! Address Book:

1. Open your Yahoo! Address Book and click "Import/Export" in the upper-right corner.
2. In the Import section, select "Netscape/Thunderbird (.LDIF file)" to indicate the kind of file you are about to import.
3. Click the "Browse" button to locate the .ldif file on your computer.
4. Press the "Import Now" button.

Please see the System and Software Requirements for Import/Export.