1. You must have both Yahoo mail and Gmail account.
2. Login to your Yahoo mail.
3. Go to Contacts – then choose import email from Facebook
4. Login to Facebook to authenticate. All the contacts will be imported automatically in your Yahoo contacts address book.
5. Export yahoo csv, then download and save it.
6. Login to your Gmail
7. Upload the csv file to Gmail contact.
There you go. If you have any other method that works better please leave your comment.