How To Sign in Yahoo with Facebook ? Read More : - https://www.yahoophonenumber.net/blog/how-to-link-yahoo-mail-to-facebook/ Sign in Yahoo with Facebook has become a matter of the past. Now it is not possible. It means, that if you have to sign in to your Yahoo account, you will require to use your Yahoo username and password. The same is true with Facebook. If you have to login into your Facebook account, you will require to use your Facebook login credentials.