I have a rebel G and have taken good fireworks pix with it. Use a tripod and set a long exposure time, 1 to even 3 or more seconds. On the G that's the Tv, for time value setting, then spin the dial till it reads 1"" or even higher. I've even done a 10 second exposure to get the climax of the show, with excellent results.
Definitely read Kelly Grannells thread at the top of this forum though, she goes into more depth.