I've confirmed this... It's an opt-out proxy in this situation (can be setup as opt-in).
https://crypto.stanford.edu/flashproxy/
> There is an options page[1] (the same page you get by clicking on the badge) with which users can choose whether they want to be a proxy. By default, if a user has not made a choice, they will be a proxy. If you want only people who have explicitly clicked "yes" to be a proxy, add the cookierequired parameter. If a user has selected "no," they will never be a proxy, regardless of the presence of cookierequired.