Facebook passwords not case sensitivegmerideth writes "A client just pointed out the following, which I've confirmed. Given a facebook password of "myPassword1234", you can log into facebook using the following password "MYpASSWORD1234" — as long as every character is the opposite from the original, facebook will still allow you to login.
"MYpassword1234" wont work but reversing each case to the example above of "MYpASSWORD1234" does work. I created a temp password on facebook of "1qaZ2wsX3edC" (having ZXC in caps) and was able to log into facebook with the password "1QAz2WSx3EDc" (with zxc in lowercase) reversing the case of each character.
I'm not sure how one would make this work other than through direct functionality versus a database query or a php method that does this."