title: Cookie “PHPSESSID” will be soon treated as cross-site cookie against <file> because the scheme does not match
body: <p>I've just noticed my console is littered with this warning, appearing for every single linked resource. This includes all referenced CSS files, javascript files, SVG images, and even URLs from ajax calls (which respond in JSON). But not images.</p>
  <p>The warning, for example in case of a <code>style.css</code> file, will say:</p>
  <blockquote>
  <p>Cookie “PHPSESSID” will be soon treated as cross-site cookie against “http://localhost/style.css” because the scheme does not match.</p>
  </blockquote>
  <p>But, the scheme doesn't match what? The document? Because that it does.</p>
  <ul>
  <li>The URL of my site is <code>http://localhost/</code>.</li>
  <li>The site and its resources are all on <code>http</code> (no <code>https</code> on localhost)</li>
  <li>The domain name is definitely not different because everything is referenced relative to the domain name (meaning the filepaths start with a slash <code>href=&quot;/style.css&quot;</code>)</li>
  </ul>
  <p>The Network inspector just reports a green <code>200 OK</code> response, showing everything as normal.</p>
  <p>It's only Mozilla Firefox that is complaining about this. Chromium seems to not be concerned by anything. I don't have any browser add-ons. The warnings seem to originate from the browser, and each warning links to view the corresponding file source in Debugger.</p>
  <p>Why is this appearing?</p>