Yes, FIRETHORN is a Scrabble word!

Letter values in Scrabble US: F 4, I 1, R 1, E 1, T 1, H 4, O 1, R 1, N 1.

Is it a valid word?

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

any of various thorny shrubs of the genus Pyracantha bearing small white flowers followed by hard red or orange-red berries

Also: fire thorn.

Not playable in Scrabble US: PYRACANTH.