I had the same issue as above! It seems like most of the problems I’m having are coming from Mozilla Firefox 49.0.1. I’ve switched to Chrome Version 53.0.2785.143 m (64-bit), kept the code as-is, and hit “run,” and it passed.
I’ve also been having this issue, in both Firefox and Chrome. I have a slightly older version of Chrome though, now trying to update if the latest is available for Ubuntu