An incendiary.
1872. Why, those chaps that are setting folks on to burn us all up in our beds. Political firebugs we call em up our way. Want to substitoot the match-box for the ballot-box.Holmes, The Poet at the Breakfast-Table, chap. i. (N.E.D.)
1883. It is believed that there exists an organized band of firebugs.Pall Mall Gazette, Sept. 6. (N.E.D.)
1888. The last of the trio of fire-bugs arrested last fall was removed to the insane asylum.Missouri Republican, Feb. 22 (Farmer).
1909. It has been decided that yesterdays first fire was not due to the torch of the fire-bug.N.Y. Evening Post, April 15.