If you have an SLR get it off programme mode and get it on a tripod. Choose manual exposure and dial your shutter speed around to b or bulb setting. On 'bulb' your shutter will stay open for as long as you depress the shutter button. Have a thick piece of black card ready. When the first firework bursts begin the exposure then carefully place the black card in front of the lens with the shutter still open. Remove the card for the duration of successive fireworks to give you a colourful multiple exposure on a single frame. Thus saying, I didnt need to do that here. Funchal bay in Madeira has one of the most extrordinary NYE fireworks displays in the world. The hills are spectacularly aflame. I bet you can see it from space.