Automatically Login to Facebook with your Gmail or Yahoo Account

Facebook has come up with a new technique where you can automatically login to it with the account you are currently using.

Now, if you login to any of the services like Google, Yahoo, MySpace, your account in Facebook will automatically login to the currently working account. This means that next time there is NO NEED need to type your login ID and password all over again!
How to set up this privilege:
To set up this privilege between Facebook and Yahoo/Google Accounts, just
Go to Facebook -> Accounts Settings
Click on "Add a new linked account".
This will login automatically to the current service you are using.
Facebook will let you link only one account at a time. For example, if you are sending an email via Gmail to anyone and using Yahoo answers, then it will ask you which account to link and thus, you can link to the respective account.