Took me a minute to realize this is developed for use with Firefox Developer Edition. If you're using Chrome or vanilla Firefox, you're going to be a bit lost when trying to follow the tutorial.
Well, it seems like it was created for the launch of Developer Edition v44, so that would have been when the stable release was v43. The current stable release is v44, so in theory everything in this demo/tutorial should work with current stable. I found a couple things didn't, though. I couldn't get the CSS eyedropper tool to apply the color I clicked on; however, manually entering the hex code for the new color triggered the completion event. I also couldn't get the event to fire in the second-to-last task.
Regardless, it's a neat little distraction to do while eating lunch.
I noticed a weird behavior with the eyedropper but it did work, partially. For me, it worked when the inspector was side-docked in the window, but not when it was free-floating.
Firefox's devtools are available in all maintained versions of Firefox. Why would Mozilla restrict devtools to releases? How would people test the devtools in that case?
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.
An add-on crashing Firefox is definitely a bug on our end, even if it's also a bug in the add-on. :) I've filed https://bugzilla.mozilla.org/show_bug.cgi?id=1221273 to track this, but I can't reproduce the crash myself. The page doesn't use React, FWIW.
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.
That's an awesome idea! To mix the knowledge, I learned some things. There needs be another for Chrome, and it'd teach all kind of tricks, and with an unknown reward at the end. This is good, this is artful teaching. Reminds me of the hacking challenges.