As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS NOT GROUNDED. RECEIVED FIRE WARNING FROM FORWARD LAVATORY, LASTED ONLY 3-4 SECONDS, RESET ON ITS OWN. IN FLIGHT FL300. MAINTENANCE PERFORMED OPERATIONAL TEST ON FORWARD LAVATORY SMOKE DETECTOR PER AMM 26-17-00. ACCOMPLISHED SATISFACTORY OPERATIONAL CHECK.