Can you tell by looking at the fuse box which circuit (fuse) was involved in the fire?
If so, check to make sure that the correct fuse was inserted. Not too high of an amperage that is. If you cannot tell which caused it check them all. Usually a fire in the fuse box is caused by a fuse that overheated and caused a fire. Now that doesn't mean that is the entire problem, there is also the cause of the overheating, such as a short circuit. So if you find out which fuse it is, tell me and I'll see if I can get a wiring diagram of that circuit.