Frame widget with changing urls

Hello,

my idea is to display in one frame two different web pages changing by time.

Therefore I defined an item:
String frame_url

and a rule:

rule "Webseiten im Habpanel Frame wechseln"
when 
Time cron "0 * * ? * *"    //every 1 Minute for testing
then 
//die beiden URLs fuer den Wechsel 
var String cam = "http://192.168.100.72:9000/?action=stream.html"
var String map = "https://goo.gl/maps/HKhpna2wD5U2"
var String frame_status = frame_url.state.toString
if ((frame_status == "UNDEF") || (frame_status == cam)){
    logInfo("urls.rules - frame_url danach", "undef oder cam")
    frame_url.postUpdate(map)
} else { frame_url.postUpdate(cam) 
}    
end

So far so good BUT but only the live stream of the webcam is shown. Why the frame widget is not showing normal webpages?

Thanks