And if so, what state of matter is it?
Huh? Why are you asking the question if you're not going to listen to the answers?It doesn't behave like typical matter, which makes some people believe that it is not actually matter.
TryDead link (at least for me), I'm afraid.
I vote for "fire is matter". Heat is heat and light is light. Heat and light is not fire. Fire is matter undergoing a rapid chemical reaction.