Your webclient questions
There may be a bug in play causing this issue, that will be fixed in 507.1275. If that's not it, I'd probably have to catch the issue in action to know more.
XMLHttpRequest cannot load http://xxx:9000/query. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://www.byond.com' is therefore not allowed access. The response had HTTP status code 500.
I don't think there's currently a way to globally disallow the webclient
Is there a way to update the default webclient byond_browser module without refreshing the entire control? Possibly using ajax?