2.1.85 [W3C-HTML52] Section 6.7.7. Page load processing model for content that uses plugins

V0257: Plugins are not loaded into a newly created document; instead a download is attempted

The specification states:

 ... Page load processing model for content that uses plugins
  
     When a resource that requires an external resource to be rendered is to be loaded in 
     a browsing context, the user agent should create a Document object, mark it as being 
     an HTML document and mark it as being a plugin document, set its content type to the 
     ... MIME type of the resource (type in the navigate algorithm), ... append an html 
     element to the Document, append a head element and a body element to the html 
     element, append an embed to the body element, and set the src attribute of the embed 
     element to the address of the resource.

EdgeHTML Mode

Plugins are not loaded into a newly created document; instead a download is attempted.