As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
IN FLIGHT, MASTER FIRE WARNING ILLUMINATED WITH FIRE BELL, AND THE MAIN DECK CARGO SMOKE DETECTOR NR 1 ILLUMINATED. LIGHTS EXTINGUISHED AND BELL SILENCED PRIOR TO CHECKLIST COMPLETION. VISUAL CHECK SHOWED NOTHING. NO REOCCURRENCE DURING FLIGHT. MAINTENANCE FOUND MAIN DECK SMOKE DETECTOR 1A DIRTY/DUSTY. CLEANED DETECTOR. SYSTEM TESTED OKAY.