According to Yahoo Mail blog:
In addition to importing your contacts from sites like Gmail and Windows Live Hotmail, starting this week you can now easily add your Facebook friends’ email addresses to your Yahoo! Contacts list. This will make it easy to communicate and share with the people you care about.Follow this step to Import Facebook Contacts to Yahoo Mail
1. Goto Yahoomail.com & login into your account.
2. Click ‘Contacts’ tab the top menu.
3. Click on Import Contact From other account to Yahoo
4. Click on Facebook
5. Now enter your facebook login details, then it will start Importing Facebook Contacts to Yahoo Mail
6. And you are done. You will be able to see that which email addresses and contacts were imported from you Facebook account to Yahoo.
Article source: http://www.mostlyblog.com/import-facebook-contacts-to-yahoo-mail