Unless there's some overriding state or local law (and in Alaska, I doubt there is), then there's no legal difference between advertising your gun for sale on the net, and putting an ad in the paper, or penny saver, or a card up on a buy/sell/trade bulletin board.
In order to engage in selling firearms or working on them as a business you have to have an FFL, but not if you're just selling off a few of your personal guns.
As long as the sale is in-state, you're only bound to make sure to your own satisfaction that the purchaser is not prohibited from owning the firearm you're selling. If you sell to someone out of state, the weapon must go to a licensed dealer in the buyer's state. In-state, you can ship guns to anyone also a resident of the same state, provided no local or state laws prohibit private fireams sales.