There is a creature on this Earth that does, um, kinda shoot fire. It's from its butt.
That would be the Bombardier Beetle. When threatened, bombardier beetles spray the suspected attacker with a boiling hot mixture of caustic chemicals. The predator hears a loud pop, then finds itself bathed in a cloud of toxins reaching 212° F (100° C). Even more impressive, the bombardier beetle can aim the poisonous eruption in the direction of the harasser.
The beetle itself is not harmed by the fiery chemical reaction. Using two special chambers inside the abdomen, the bombardier beetle mixes potent chemicals and uses an enzymatic trigger to heat and release them.