Lightly grease two baking trays.
Cream the butter or margarine with the sugar until very soft, light and fluffy.
Sift together the flour, cornflour and salt, then gradually work these dry ingredients into the creamed mixture - the resulting paste should be just soft enough to pipe.
Divide the mixture into three, then work a different food colouring into each portion.
Fit a vegetable piping bag with a medium sized star nozzle.
Spoon the red dough down the left side of the bag, the blue down the centre and the green dough down the right hand side of the bag.
Pipe 7.5 cm/3 in lengths of dough on to the prepared baking trays, zig zagging the mixture from side to side to represent fire crackers.
Chill the biscuits for 30 minutes, or longer if you have time.
Bake the fire crackers in a moderate oven (180 C, 350 F, gas 4) for about 15 minutes, or until darkened in colour and cooked.
Remove the hot biscuits from the trays and transfer them to a wire rack to cool completely.