As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
EICAS MSG FIRE MN DK AFT NO SMOKE OR FLAMES. CREW FOLLOWED QRH AND DEPRESSURIZED AIRCRAFT WHICH CAUSED THE O2 MASK DEPLOYMENT. R & R MCD SMOKE DETECTORS 12A AND 12B IAW AMM 26-14-01. OFF PN 2156-756A SN 20590B. OPS CHECK GOOD. MX RESTOWED ALL O2 MASKS IAW AMM 35-21-06.