When you enter the Fire Temple you will meet up with Darunia. He will tell link to rescue the rest of the Gorons. Go into the big room on the left side of the temple. Inside you will find a gate with a Goron inside. Rescue him by opening the door for him. To open the door, hit a switch. then get the key in the treasure box. Now go to the main hall. Go into the other big room on the right half of the building. Once inside go to the left half of the room and free the next Goron.

Then go straight across and free the other one. You might have to move a blue block, just use the Song of Time. Now just go and continue following the bridge to go to a new room. In there you will find a large pair of towers. Climb up the fence cage t get on the top of one of them. If you are on the correct block you will find a huge block. Push the block into the fire and voila you have made an elevator. In the new room find your way to the tip and throw a bomb over the side to set off the white crystal, then climb up the wall that was blocked by fire. This room is filled with rolling boulders. 

Find your way through and get the 3 keys and rescue the captive Goron. When you have completed this puzzle go in the next room and you will be in a room with platforms that when you touch you get followed by fire. Just KEEP RUNNING and you won't get hurt. At the end of the fire curtain you will find a ledge with the dungeon map. You may have noticed a side room while you were running from the fire RIGHT? well go in the room and you will in this huge room with a lot of poles and when you try to walk between some of them fire will rise up. Just find your way through and you will be in a small room with a key. Now continue into the next room to finish the flame maze. 

When you find your way through you will be faced with a mini-boss called Flame Dancer. To fight this foe shoot your Hookshot at it and the flame will go out then SLASH THE HELL OUT OF IT until it dies. ^_^ A hole will open that will lead you to a room that looks like stairs a little. To get the Megaton Hammer you must hit the white crystal and run to the chest before the flame comes back. Now go into the door farthest from the hammer. In the new hall just hammer the floor and the floor will turn to stairs. Follow them.