It's O.K. The side of the box is missing, so there's plenty of ventilation [Linked Image].

Now for the serious side, I had a fire call a couple of years ago in a mobile home - HO reported a strange "hot" smell. On arrival, the wall receptacle in the living room was glowing red, easily visible in the room. Same type of receptacle you picture here - relatively cheap product, 15 amp max. capacity. The one we dealt with was wired with 12/2/G copper romex, with a large window air conditioner farther down the line.
After shutting down the circuit and cutting the wall finish away from the receptacle, we found a plastic box, badly distorted from the heat, just about ready to ignite. The wiring connections to the receptacle were pretty loose, possibly from the severe heating/cooling effect.

Mike (mamills)