Flame gloves are a reward from the All Fired Up minigame. These gloves require a Firemaking level of 79 to equip, which is also the minimum Firemaking level needed to obtain the gloves.
They give a 2% bonus to experience gained through Firemaking, which will stack with the 2% bonus from the ring of fire, however, when worn with the ring of fire, the total bonus is 5%. They do not give any bonus for lighting the fire altar in the Temple of Mort'ton.
To get this reward you must light 10 beacons in the minigame and talk to King Roald in Varrock Palace. Should one lose the flame gloves, one must light the 10 beacons again to re-obtain them. Lighting the beacons again while already having the gloves does not give any reward.