It is a web-based service, the browser integrates into your dashboard which is web-based. You need to have an account to use it.

Why not make it possible to be able to sign up after you download the browser?

Like if you don't sign in/connect-the-browser-to-an-account, it'll only let you go to a few sample pages and let you mess around with a few settings. As soon as you try to do anything else, a "Please sign up" form appears.

We aren't ruling that out. However, we have made it very easy for people to try it free, without commitments of any kind.