THE FIREFLY PERK MAY CAUSE GAME CRASHES WHEN ACTIVATED ON SOME WEAPONS.
Bungie is aware that some players have encountered an issue with the Firefly perk, which may cause Destiny to crash. If you have a weapon that has caused this to happen, please refrain from using it until this issue is addressed in a future update.
Information on the latest updates for Destiny can be found here: WHAT ARE THE LATEST UPDATE/HOTFIX/PATCH NOTES?
If you experience a game crash, you may report it here: GETTING HELP WITH DESTINY GAME CLIENT CRASHES.