If you watch your browser you can see if it does or doesn't. You only need trust your browser at that point. If you don't trust your browser, you can monitor n

If you watch your browser you can see if it does or doesn't. You only need trust your browser at that point. If you don't trust your browser, you can monitor network activity as the OS level. Should provide a pretty good assurance. That said, I still wouldn't use it without (a) a private browser window, (b) taking the machine offline, and (c) killing the browser before going back online. Unfortunately, I don't think most people who will use this will do such a thing. (And I'm still not sure I'd trust it for any really serious work.)