title: Using window.opener causes CORS error
body: <p>I have an application that creates a pop-up window, which loads a page which then fetches data from the opening window, like so:</p>
  
  <pre><code>var globals = window.opener.globalsCache;
  </code></pre>
  
  <p>However, when deployed to production, this intermittently causes the following error:</p>
  
  <pre><code>DOMException: Blocked a frame with origin from accessing a cross-origin frame
  </code></pre>
  
  <p>Note that the popup window has exactly the same URL as the opener, except for the hash. <em>(i.e. https:/hostname.tld/application/#page-name )</em>.</p>
  
  <p>Has anyone seen this issue before?  Any ideas on why it is happening and how to fix it?</p>