"Toggle fullscreen" in "BookReader embed example" demo leads only to new blank tab

I cloned the repo to my local system and am on v. [5.0.0-77](https://github.com/internetarchive/bookreader/commit/cc512e7ea9ac381fa1af3bbe0386fc20be59b476). When on the "embed" demo (`/BookReaderDemo/demo-embed.html`), if I click on the "Toggle fullscreen" button, all that happens is that a new tab gets opened in my browser. I'm not sure what is supposed to happen but presumably some kind of full screen mode. I'm on Windows 10 and the same happens in Chrome 120.0.6099.130 and Firefox 121.0.