wrote:
I know that the wall between my home and attached garage is a double
thickness of drywall for fire resistance purposes.
Am I violating code or reducing the level of protection by drilling a
hole to bring out a new electrical circuit? Can I place an outlet box
in the firewall? Are there ways I can/should do this to remain
code-compliant?

I think that you'd be better off using surface-mount components and
conduit. That way you only have the one hole where you're
bringing the conduit through the wall.