title: Prevent default error message with firebase-ui
body: <p>I'm using firebase-ui and Google Identity Platform for login.  I'm using a Google cloud function to limit the email addresses that can be used to login.  It is mostly working except that I can't prevent the default ugly error message:
  <a href="https://i.stack.imgur.com/qMdEL.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/qMdEL.png" alt="enter image description here" /></a></p>
  <p>I'd like to precent this from appearing and instead use my own error message.</p>
  <p>I have a callback function that looks like this:</p>
  <pre><code>  'signInFailure': function(error) {
      console.log(error);
      //return Promise.resolve();
      //return false;
      //return true;
    }
  </code></pre>
  <p>You can see in the comments the variants I've tried.</p>
  <p>How do I prevent this error message from being shown?</p>
  <p>=== UPDATE ===</p>
  <p>Turns out that <code>signInFailure</code> is not being called.  There is some other exception handling that causes this error message to be shown.  Would be great to have a workaround, but I suspect that I just can't use firebase-ui.  :(</p>