tl;dr This is a series of interactive demonstrations showing off some of Firefox Developer Edition's developer console features, with emphasis on CSS animation.
The DevTools Challenger page is meant to be a more hands-on set of exercises to familiarize people with the new / improved animation tools. You should be able to complete it in regular Firefox (or even Chrome), but the experience will be a bit nicer in DevEdition.
Not too sure if is this something that should be reported to Mozilla or to Facebook.
If you could stop by that bug and leave a comment with your OS, Firefox version, and build info from about:support, I'd appreciate it.