The dialogue box is the result of
     <head>
      <!-- ... -->
      <meta 
        http-equiv="Content-Script-Type"
        content="text/javascript" />
      <!-- ... -->
     </head> and
        <body
       onload="alert('This is the JavaScript version.')">
     <!-- ... -->
    
   Content-Script-Type be present?
      head?onload?
      onLoad (with uppercase L) instead?