This is something I do quite often....Throw your firecracker at something that will deflect it to the intended target. It's especially useful if you're on top of a building and you are trying to eliminate some pesky Prefects or stupid Cops that are right below.
Target your firecracker to hit the edge of the building you're on. It will 'Bounce' up and then drop straight down over the side. BAMM !
Target something for the firecracker to ricochet off of. Example is the Oil Spill Gas Station. Target the edge of the apron over the gas pumps. It will bounce off, at the right angle, to hit the Cops right below. BAMM !
I could...and have....Done this for hours.