How about Oxford Dictionary?
Definition of Gun
https://en.oxforddictionaries.com/definition/gun
A weapon incorporating a metal tube from which bullets, shells, or other missiles are propelled by explosive force, typically making a characteristic loud, sharp noise
Definition of Firearm
https://en.oxforddictionaries.com/definition/firearm
A rifle, pistol, or other portable gun.
Now, tell me, is this Greek Fire, invented in 670 AD (230 years prior to Gunpowder), a firearms?
View attachment 424228
According to Oxford Dictionary, yes.
An Fire arms is a portable gun, and a gun is, according to oxford dictionary, a metal tube from which bullets, shells, or other missiles are propelled by explosive force, Greek Fire uses sulphur to propel burning arrow/missile toward the enemy, and is portable as shown in the picture, hence according to Oxford Dictionary,
GREEK FIRE IS A FIREARM
And yes, Wikipedia can be wrong, so,
YOU ARE WRONG IN THIS CASE. Or are you telling me Oxford Dictionary is wrong?