Craiger... chill.

Using an Off GCD ability on your last fire spell forces the game to register if you have a firestarter proc immediately. Don't insult others if you don't know what they are talking about.

Fire 3 > Fire 1 > Fire 1 > Fire 1 > Fire 1 > Fire 1 > Lethargy as Fire 1 is finishing, clipping the cast time > Tap Fire 3 > You use a Firestarter the instant the Fire 1 is cast.