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

First, export your contact data from Yahoo! Address Book:

1. Open your Yahoo! Address Book and click "Import/Export" in the upper-right corner.
2. In the Export section, click the "Export Now" button next to the phrase "Netscape/Thunderbird".
3. A dialog window opens and gives you the option to save your Yahoo! Address Book to disk as an .ldif file. Click "Save to Disk".
4. Click "OK". The .ldif file will be saved to your desktop.

Next, import that file into Thunderbird:

1. Open Mozilla Thunderbird version 1.0 or higher.
2. Open the "Tools" menu and select "Address Book." In the Address Book window, open the "Tools" menu and select "Import."
3. Under "Select the type of material to import," select "Address Books." Click "Next."
4. Under "Please select the program from which you would like to import," select "Text file (.ldif, .tab, .csv, .txt)." Click "Next."
5. Locate the .ldif file to import. For "Files of type," make sure that .ldif is selected. Click "Open." That's it! Done.

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