The firefighter has admitted to setting fire to twigs using gasoline and a lighter, according to Franceinfo.
The Seine-et-Marne department's fire service said in a statement that it views the fact that the fire was started by a volunteer firefighter as "particularly serious" when scores of firefighters "have been fighting fires of exceptional magnitude for several days."
On Tuesday, the fire service announced that the fires in Fontainebleau were under control, but not extinguished. Around 2,000 hectares of land have been ravaged by the fire.
