I just tried it again on the Mac, this time with a shallow browser window. It worked. My previous window was close to 1600px high.
I noted earlier that it worked fine on Ubuntu using an old version of Chrome. That machine's monitor is 1360x768.
1. In Chrome, the "Audio Narration Off" was offscreen. I had to resize the browser to hit that button. Then it wouldn't show any content.
2. It worked just fine on my iPad. So maybe try a mobile device instead.