I hadn't heard the term 'firing' used for arson before. Since it was used in the context of the police, and if it is a term they use, then I would consider it appropriate. It also would depend on how it is used. Some writers, TV show, movies etc. used terms or phrases to add 'ambiance' if you will. Others seem to beat it to death to prove they are experts of the culture or such.
Just think back to say 'Shogun', how many people knew what a 'Shogun' was before. Do we change the term or keep it to add an element of the culture.
Tom