For fireworks, one thing to keep in mind is you are photographing brightly burning embers in flight. You don't need a high ISO to record brightly burning embers. If you set your ISO very high, you will pick up ambient light sources and the sky will be a muddy gray instead of black. You're better off trying a relatively slow ISO speed.
Another tip: If you're fairly close to the display, you'll hear the boom from the launch of the firework. Shortly after you hear the boom, you want to open the camera's shutter in anticipation of the burst. If you open up the shutter when you see the burst, the resulting image will have an empty spot in the middle of the burst. Also, if you open the shutter before the burst, often you will capture the light trails of the "shell" as it rockets skywards, which is a cool effect all in itself.
To do all this effectively with the Canon XS, you really need a remote shutter release, like the Canon 60 T3 -- or equivalent aftermarket product. Needless to say, you'll need a tripod too.
In the past, when I've shot fireworks, I would set the ISO to 100 or so, stop my lens down at least to f/8, set the camera to "B", and with a remote release, trip it when I heard the boom, and release it after the last ember faded.
Try it. It works really well. If for some reason, it doesn't work with you (which I doubt, really), it will at least give you a baseline from which you can make changes until you're getting the images you want.