Navigating to the `firebase-auth` demo page and choosing the provider type "Google" results in a Unauthorized Request Origin error page from Firebase. <img width="400" alt="screen shot 2016-05-16 at 8 28 45 pm" src="https://cloud.githubusercontent.com/assets/719730/15310463/eb3c9aea-1ba4-11e6-8b47-7655f0d3bc7b.png"> Reproduction steps: 1. Navigate to [firebase-auth demo page](https://elements.polymer-project.org/elements/firebase-element?view=demo:demo/index.html&active=firebase-auth) 2. Choose "Google" in dropdown 3. Click Login