for the fire?
simple:
gas bladder to expel some flammable gas in a "jet" (lets say methane or hydrogen for the fliers, also doubles in letting them fly by giving them extra lift, both of which are naturally created by acteria living in many animal's stomachs) through some pore in their mouth or such.
near this pore will be ome sort of means of ignition, a special tooth or even minerals the animal collects to start the fires witha small spark by rubbing the minerals/teeth together.
the gas is jetted out while the creature creates the spark, and the jet of gas is ignited just like a flamethrower. granted, the animal may want a shut-off valve through the nozzle to prevent back-draft.
in short, a natural flamethrower would work just like a real one, only substituting a gas canister for a special bladder and a lighter for a manual spark.