I don't see a license file nor a license in extension.js or README.md.
Yeah, I guess I should choose one. It'll probably just be BSD or MIT, after I read about them and get a better understanding of software licensing.
MIT and BSD (2 or 3 clause) are both good.
If you do choose BSD I'd recommend the Simplified BSD (2 clause) over the Modified BSD (3 clause). The BSD wikipedia page makes the differences pretty clear.
Whatever you choose, make sure to clear the license with current contributors.
This might help: http://www.opensource.org/licenses/category
adding MIT license Closes #4