How to Set a Firmware Password on a Mac with macOS Mojave, Sierra, OS X El Capitan, Mavericks
Mac users in higher security risk situations may wish to enable an optional firmware password on their machines,which offers an advanced level of protection. In short, a firmware password is a lower level layer of security that is set on the actual Mac logicboards firmware, rather than at the software layer like FileVault encryption or the standard login password. The result of setting an EFI password is that a Mac can not be booted from an external boot volume, single user mode, or target disk mode, and it also prevents resetting of PRAM and the ability to boot into Safe Mode, without logging in through the firmware password first. This effectively prevents a wide variety of methods that could potentially be used to compromise a Mac, and offers exceptional security for users who require such protection.