I also have this exact problem. I have tried several browsers, disabled all firewalls and updated everything I can think of (even my built in webcam's Firmware).
The problem appears to be something to do with the plug-in attempting to enable the webcam. I have an LED next to my webcam which comes on when it is in use, this does not come on when attempting to load the scenario. Other web-enabled applications are able to initialise and use the webcam with no problems (http://www.chatroulette.com
is an example)
Interestingly, if the AR page is refreshed after it hangs, the webcam is enabled for about a second before it goes off again and the process hangs in the same place.
In firefox, if the add-in is disabled after the process fails to load, a menu becomes apparent behind the AR frame. This lists available webcams but it is impossible to select one as the add-in is not running. Re-enabling the add-in and refreshing the page then leads us to the same stalled window.
Hope this additionall information is useful to someone and that this can be fixed.