Okay, real answer. First of all, you'll never be able to avoid piracy. Nature of the medium. Second, the best way would be to embed individual user credentials

Okay, real answer. First of all, you'll never be able to avoid piracy. Nature of the medium. Second, the best way would be to embed individual user credentials into the extension. As in, they signup and pay or whatever, and you generate a unique extension that contains their authentication information, which they then install. What is this for?