I was using the itch.io app and it doesn't seem to play the browser games it in... maybe I need Flash? (which I definitely don't have).
Edit: just tried it again and the itch.io app has me install it; the error is:
"Unable to parse Build/WebBuild.framework.js.gz! This can happen if build compression was enabled but web server hosting the content was misconfigured to not serve the file with HTTP Response Header "Content-Encoding: gzip" present. Check browser Console and Devtools Network tab to debug."
Hmmm... doesn't look like Flash, maybe Javascript is being blocked somewhere?