This one is from 1905:
Bayonne Man Admits Burning 15 Houses, Police Say. HE LOVED THE EXCITEMENT Never Missed Responding to an Alarm and Was Always First at the Engine House.
March 27, 1905, Monday
The police of Bayonne yesterday afternoon arrested James McInerny, a member of Americus Engine Company of that city, and later declared they had obtained from him a confession that he had for months been starting fires for the sake of fighting them when the alarms were turned in
http://query.nytimes.com/gst/abstract.html?res=950DE7DE173DE733A25754C2A9659C946497D6CF
More recent cases:
Too Close To The Fire
A Problem Few Firefighters Want To Talk About
http://www.cbsnews.com/stories/2002/11/20/60II/main530103.shtml
We’ve had a couple of firefighter/arsonists in Seattle, including a rather a notorious one who committed over 60 fires. He eluded police until four firefighters perished in a warehouse he had torched. He was caught and sentenced to 99 years. I know that there were many who thought that he deserved to “ride the lightening”.
I recall being one of them...