As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE, NR 1 ENGINE FIRE WARNING CAME ON, CREW SHUTDOWN NR 1 ENGINE AND DISCHARGED BOTH FIRE BOTTLES. RETURNED AND LANDED WITHOUT FURTHER INCIDENT. MX INSPECTED AND FOUND LOW RESISTANCE FROM NR 1 FIRE DETECTOR PIN L TO GROUND. MX REPLACED NR 1 FIRE DETECTOR CONNECTOR AND LT PYLON LOOP CONNECTOR AND BOTH FIRE BOTTLES. OPERATIONAL CHECK GOOD IAW MM 26-10-0, AND 26-20-1. AIRCRAFT WAS RETURNED TO SERVICE.