Other than guns for bimbos what is a "fire-stone"?

Bad translation perhaps for cartridges or perhaps the age of the advert was still in the transition between cartridge and muzzle loading firearms?

Judging from the other language versions "fire-stone" (German "Feuerstein" or "flint") meant "flintlock". However the French version says "percussion", which would indicate "cap-lock". In any event, "muzzle loading".