Before starting the method you should remember that you will not use this method for wrong things.
You must have a good dealing, to perform this method on your friends.
So lets start with the method.
1- You have to download a software named as Family key logger.You can download it from http://www.spyarsenal.com/.
2- Install the software and run it. The key logger icon will be visible on your screen at bottom right corner. You may have to disable your antivirus for just 10 minutes.
3- Now you have to ask your friend to open his Facebook account,you don't have to see his password.
4- After some time when your friend has gone then,you can right click on the key logger icon and click on view blog.
5- Now you can see all the letters which your friend has typed on your keyboard and obviously his Facebook's email id and his password will also be written there.
Congratulations, now you can see what your friend is doing with your machine and also what he is doing on the social site Facebook.