Firmware password protection requires a password to boot from an external source. Doing so, give the operator the capability to reset the admin password. Once that has been done, the user can then boot from the device itself and have access to all the admin functions, install/remove apps, etc.
By default, the firmware password is disabled. If you forget your firmware password, removal of RAM will turn off firmware, so know that if you have removable RAM, any other person could do the same thing. There are many new models of Macs that have soldered in RAM (AIR's, to be specific), so a reset of firmware password would have to take place by an authorized Apple dealer
To set up a firmware password, you will ned to boot your device from an external startup disk. If you are running 10.7 or later, choose the "Recovery HD." Once you have done that, go to the Utilities menu at the top of the screen.
e screenOnce you have entered the firmware password and confirmed it, restart the Mac normally. Then this password will be required to start up the Mac from an external drive.
To disable your Mac’s firmware password, follow these instructions and deselect theRequire password to start this computer from another source checkbox in the Firmware Password Utility.