Firewhiskey is an alcoholic drink that is consumed by wizards and witches. Those under the age of seventeen are not allowed to buy it, implying that they may not be allowed to drink it. This rule is not always followed. Popular brands include Ogden's Old Firewhiskey and Blishen's Firewhisky. It is known to cause a burning sensation when drank, and for filling one's body with courage.
Ron Weasley commented that he could most likely purchase Firewhiskey at the Hog's Head during the Dumbledore's Army meeting. Hermione was angered at that, furiously reminding him of his prefect status. He instead had Butterbeer.
After reaching The Burrow after departing Number 4, Privet Drive, Harry Potter drank a toast to Alastor Moody's memory with Firewhiskey, served by Bill Weasley, a few days before Harry's seventeenth birthday.