Firecracker has been an awesome tool for offensive strategies for me. It's particularly effective in manhunt. In my limited experience, I notice that using it causes all the NPCs to fall and cover their eyes while any player characters will stand dumbly looking obvious.
On the receiving end, do players affected by firecracker experience a white screen? I've been blinded several times like this, and while I don't lose control (I've both evaded and assassinated while blinded) I can't see anything. I wasn't sure if this was a seperate ability or the same one.