FIREFLY - Precision kills with this weapon cause the target to explode.
Precision kills cause a 50 damage Solar blast in a 5 meter radius
In Destiny, FIREFLY is a Weapon Upgrade that can be found on Legendary Scout Rifles and Sniper Rifles in the game. Weapons in Destiny pull each Upgrade at random from specific pools (with a few Weapons that are an exception). Killing an enemy with a headshot creates a 5 meter explosion of Solar Damage.
To see more info on exactly which Weapons this Upgrade can be found upon click the link below:
To see more about how this Weapon Upgrade fits into these pools, please click the links below:
SNIPER RIFLE WEAPON UPGRADES
SCOUT RIFLE WEAPON UPGRADES