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Pretty cool to see a screenshot of CodePen on The Mozilla Blog. It comes from them showing off the new performance tools in Firefox Developer Edition. Part of that was a game they created called Power Surge. It's here on CodePen!

See the Pen Power Surge by Mozilla Hacks (@mozhacks) on CodePen.

It's a pretty fun little game. But the important part is that they created it with intentionally unoptimized JavaScript. You can then use their new performance tools to identify those areas and improve it.