Boot with Option key held to display the boot menu's firmware password prompt.
Press Control-Option-Command-Shift-S to reveal a 33-digit hash (mixed letters and numbers) that contains an identifier for your specific motherboard and the Atmel chip used for your system. In this hash, the first 17 digits are an identifier for the system's motherboard, and the last 16 digits are a hash for the password.
Submit the hash to Apple, where someone will put it through a special utility to create a keyfile that is specific for your machine.
Place the file on a special USB boot drive and hold Option to load the boot menu and select this drive.
The system will read the file and properly reset the firmware password stored in the Atmel chip on the logic board, which contains the firmware password.
This process may seem easy enough, except that the utility for creating the keyfile is kept at Apple so you have to go through an authorized service center, which will contact technicians at Apple for this service. Secondly, the Apple technicians will not give you the keyfile for unlocking your system, so you must get your system serviced to perform this step.