In the episode The Earth Queen just before Gombo and his gang attack Korra and Asami a sign can be seen in the sky. It looks like a signal from a flare gun. It could also come from a firebender but I doubt it. Knowing that there are fireworks in the World of Avatar, and if that really was a flare gun, do you think that eventually we might see firearms?
Well when gunpowder, to make fireworks, was discovered in the Bending World guns should have followed like it did in our world. However I think thanks to the part that bending exist I don't think such an application came to be, however I do remember the Fire Nation's lighter-than-air aircrafts having small cannons used to shoot explosive artillery during one episode in the original show. Yet thanks to censorship of such things in animations aimed at children to young adults I would not bet on those kinds of weapons ever appearing on this or any follow-up series and/or spin-offs.
Jey8000 wrote: Well when gunpowder, to make fireworks, was discovered in the Bending World guns should have followed like it did in our world.
Not necessarily. Guns are not flares. Guns are scaled down cannons, and cannons of this world are based on firebending (a firebending gun isn't that useful because you'd still have to go through the motions for very little benefit). Crossbows and swords are a bit more useful.
Considering with how technology in the Bending World is going, they'll probably skip traditional firearms altogether and jump to railguns (or rather crossbows with magnetic accelerated bolts). However, considering that technology seems to be aiming towards the fantastical, we're more likely see tesla guns.
We've seen the Dai Li use super-fast chunks of earth in a manner similar to bullets. We've seen flamethrowers (both mechanical and literal). We've seen a GIANT SPIRIT WEAPON that is, effectively, an atomic cannon. And, of course, we've seen general Bending, scaled down or not, and more importantly, METALBENDING. As in, stopping bullets in mid-air?
Let's face it, while the potential is there, nobody, not even the Fire Nation during the Hundred Year War, ever thought of building a gun, because a) it would even the playing field too much (in war and in peace), and b) there are already too many equivalent or superior methods of attack. Guns, very simply, are not a part of the Avatar world, regardless of whether it's a kid's show or not.