title: Firefox 68: local files now treated as cross-origin; is there a way to override?
body: <p>Firefox 68 fixes a security problem with local files (<a href="https://www.mozilla.org/en-US/security/advisories/mfsa2019-21/#CVE-2019-11730" rel="noreferrer">https://www.mozilla.org/en-US/security/advisories/mfsa2019-21/#CVE-2019-11730</a>), but in so doing breaks testing code locally. Is there a way to override this as can be done with Chrome and Opera (e.g., --allow-file-access-from-files)?</p>
  
  <p>I cannot find anything relevant on the Firefox site, and cannot find a suitable command-line option or anything in about:config.</p>
  
  <pre><code>try {
      main = opener.document;
      }
      catch (e) {
      console.log(e);
      console.log(e.name);
      }
  }
  </code></pre>
  
  <p>I get the following messages in the console:</p>
  
  <pre><code>DOMException: "Permission denied to access property "document" on cross-origin object"
  SecurityError
  </code></pre>