As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
INSPECTION TYPE-N/A, DURING CRUISE MOMENTARY MASTER FIRE WARNING LIGHT ILLUMINATED AND BELL SOUNDED. UNABLE TO DETERMINE THE SOURCE, ALL FIRE SYSTEMS TESTED NORMAL. DID NOT OCCUR AGAIN. INSPECTED FIRE WARNING LOGIC CARDS, NO DEFECTS NOTED.