Examples from the Web for firebox
The shirt followed the leggings, after which, with a dull clanking of the stove lids, he covered the firebox.The Rich Little Poor Boy|Eleanor Gates
As there is no firebox, the boiler is mounted above the axle, not by bolting a plate to the side of the firebox.
He cooked himself an excellent supper, toasting bread and frankfurters in the firebox of the roller.Where the Blue Begins|Christopher Morley
In a locomotive boiler the mud accumulates in the water leg, below the firebox.
Beam axle of the engine is behind the firebox, and is a single solid steel shaft.