Kongregate does not control what adverts are displayed. Their regional advertising partners do that. All Kong can do, is state acceptable age-appropriateness, and ask providers to remove infected or otherwise harmful advertisements.
Depending on where you live in the world, and what interests you have previously looked up on the computer, your adverts will change. You have obviously looked at firearms before, and so the advertising agencies that track what sites your computer has visited, display gun-related adverts on the site.
If you wish to get rid of them, delete the advert-company cookies from your computer (as that’s what’s tracking what sites you have been to), or install an ad-blocker to remove adverts entirely.