The iconurl conrol, retrieves the value of the ICON parameter in the STATS XML tag, when ever a new page is loaded in the browser. This is done by the GetXMLVAlue() function. This controls is pernamently hidden and its function is to retrieve and store the icon link.
When ever the value of the iconurl control changes, the the onchange trigger calls the SetIcon() function which changes the icon of the test toolbar button.