Firebuilding would be an acceptable term if there is no actual word. "Your skill in 'firebuilding' increased" sounds a lot better than "Your skill in 'instigating fires to come into existence' has increased."
Firebuilding would be an acceptable term if there is no actual word. "Your skill in 'firebuilding' increased" sounds a lot better than "Your skill in 'instigating fires to come into existence' has increased."