What was found
#2 ENGINE FIRE INDICATION ON THE GROUND, AT IDLE, PRIOR TO TAKE OFF. QRH WAS FOLLOWED AND FIRE BOTTLE #1 DISCHARGED. INDICATION REMAINED SO FIRE BOTTLE #2 WAS DISCHARGED AND EMERGENCY DECLARED. AIRPORT FIRE RESCUE RESPONDED AND FOUND NO INDICATION OF FIRE. AIRCRAFT RETURNED BACK TO THE GATE. MAINTENANCE FOUND NO INDICATION OF FIRE. REMOVED AND REPLACED ZONE 2 FIRE DETECTOR ASSY (FIRELOOP) I/A/W B767 AMM 26-11-02. CONDUCTED AN OPERATION CHECK I/A/W B767 AMM 26-11-00. OPS CHECK GOOD. ALSO REMOVED AND REPLACED #2 ENGINE FIRE BOTTLE AND CARTRIDGE #1 AND FIRE BOTTLE AND CARTRIDGE #2 I/A/W B767 AMM 26-21-03. OPS CHECK GOOD.