As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
EWR - FL 274 - AFTER TAKEOFF FROM LGA, CREW RECEIVED MASTER CAUTION AND THE LEFT ENGINE FIRE WARNING. THE FIRE WARNING EXTINGUISHED WHEN THE THROTTLE WAS RETARDED. FLIGHT DIVERTED TO EWR AND LANDED WITH NO FURTHER INCIDENT. MAINTENANCE REPLACED A BLOWN 13TH STAGE DUCT. (X)