Works fine on firefox desktop for me. Its some kind of locale issue I think, as others have suggested.

It appears/functions on iOS Safari just fine.

Firefox on android has a checkbox in the menu for Request desktop site. Then it loads the spinner.

I had to request the desktop site on firefox mobile to be able to see it...

Once the spinner picks the right number, a code is revealed.

Nor does firefox on desktop. Chromium did work though.

Safari 10.0 works fine as well.