I'm actually surprised that anyone ever tried to roll Firefly on Timur's Lash. I knew from the beginning that Firefly only showed up on Scouts and Snipers, because the strategy guide clearly says so. But even if I hadn't read the guide, a month of Destiny pretty much assured me that Firefly was only for those two guns. I feel sorry for anyone who wasted tons of motes trying to it on the Lash though. Hopefully this post prevents any future mistakes like that.