I have an iMac I bought from Best Buy in 2011. I moved around the world and country over two years and left it with my mother. Prior to doing so, I set a firmware password. I've forgotten it. I've been able to access my account, login, upgrade MacOS, etc., it only requires the password if I attempt to boot with arguments, i.e. recovery mode. Best Buy only archives purchase invoices for three years. Apple won't assist with the unlock without an invoice. I've basically just settled with the fact that I can use my iMac, but can never use safe mode, target disk mode, etc. I made a mistake. When upgrading it to macOS Sierra, I thought I had a work around. I created an OS installer USB, used terminal to flag the computer in target disk mode (thinking if it didn't work, long shot, I could just turn off the computer and turn it back on--the OS would load as normal). It didn't work. Now it's stuck trying to boot in target disk mode, which requires the firmware password. Turning it off and on does not reset the target mode argument at boot. It keeps trying target disk mode, resulting in demands for my password. Is there an argument that can be made or something I can do to make the iMac boot normally, so it will stop asking me for my firmware password and allow me to login?