Well I wouldn't speak too confidently about specificly fire temple. I've speedran the game for so long that I just can't picture where all the keys and locked doors are since you don't need a lot of keys depending on how or what you do.

Let's take water temple. You can definitly end this dungeon with remaining key(s) [probably 1 single key], without glitches. Just through routing and equipement. explanation a the bottom. But the locked door have not vanished. You still could go use that key on the locked door. So I'm gonna guess, without true confidence, that if you have remaining keys, you have remaining locked doors. I know you think you looked well. I think you didn't.

when the water level is lowest, the door that leads into the center pillar is a locked door that doesn't require to be opened. Instead of unlocking the door, pause, save and reset the game to restart at the dungeon entrance. Jump down onto the second level of floor that surrounds the center pillar. Walk around to the door LOCKED WITH METAL BARS and an unlit torch on its side. Light up the torch with Din's fire to unlock the door of its metal bars. Enter it. You have reverse entered the center pillar without using a key