Facebook Allows user to use three different passwords to Log in.
Suppose Your password is HackBlitz
The First Way of Logging is use the same password as it is i.e HackBlitz .
The Second way of logging is just reverse the Case of your password i.e Uppercase letters to Lower case and lower case letters to upper case. So, the second password for logging is hACKbLITZ just reversing the order.
The Third way of Logging is to make the the first letter of your password to uppercase suppose your password is hackBlitz then you logging as HackBlitz making the first letter to Uppercase.