Yes, FIREWORK is a Scrabble word!

Letter values in Scrabble US: F 4, I 1, R 1, E 1, W 4, O 1, R 1, K 5.

Is it a valid word?

FIREWORK is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

(usually plural) a device with an explosive that burns at a low rate and with colored flames; can be used to illuminate areas or send signals etc.