chore: add CustomStateSet Mozilla issue link

Author: calebdwilliams

reports/2022.html

@@ -1330,10 +1330,10 @@ <h3>Links</h3>
                 <strong>Chrome</strong> &mdash; shipped
               </li>
               <li>
-                <strong>Firefox</strong> &mdash;
+                <strong>Firefox</strong> &mdash; <a href="https://github.com/mozilla/standards-positions/issues/688">Mozilla position (GitHub issue)</a>
               </li>
               <li>
-                <strong>Webkit</strong> &mdash; <a href="https://github.com/WebKit/standards-positions/issues/56">WebKit position</a>
+                <strong>Webkit</strong> &mdash; <a href="https://github.com/WebKit/standards-positions/issues/56">WebKit position (GitHub issue)</a>
               </li>
             </ul>
           </dd>