Find out the friends of a friend, although they are private and invisible.
How to:
// Step 1: Go to the profile on a friend
// Step 2: Manually scroll down the page. The more you scroll, the more friends you find out
// Step 3: Open the javascript console
// Step 4: Paste jQuery code
// Step 5: Paste this file
// Step 6: write "outputFriends()" into the console