VEHICLE WAS STOPPED ON A SLOPED DRIVEWAY, MOTOR RUNNING, IN PARK. DRIVER WAS STANDING OUTSIDE THE CAR WITH DRIVER DOOR OPEN ATTEMPTING TO ADJUST DRIVER SEAT POSITION. PASSENGER REACHED OVER AND PUSHED START/STOP BUTTON (DID NOT CONTACT THE SHIFT LEVER). VEHICLE STARTED ROLLING BACKWARD,ACROSS STREET INTO NEIGHBOR'S DRIVEWAY AND THEN CAME TO REST IN THE MIDDLE OF THE STREET. DRIVER DROPPED AND ROLLED AND SUSTAINED MINOR INJURIES(SCRAPES AND BRUISING) NO POLICE REPORT FILED.