High CPU/Memory usage in challenges/talk-throughs

(Reported on Zendesk)
"I've been programming in Khan Academy recently with my 2013 Macbook Air, and for some reason the website uses over 100% of my cpu and my fans start speeding up to over 6000 RPM.

Does anyone know any solutions to this problem? I noticed that Pamela from the Khan Team uses a Macbook, so there must be some way to avoid this.

Thanks in advanced!"
https://khanacademy.zendesk.com/hc/communities/public/questions/202860364-Macbook-air-fans-going-CRAZY-while-coding-JS-in-Khan-Academy

I use Khan Academy on a Mac without any problems at all, and I know a few people who use it on Macbook Airs without any issues like this.

I've asked for more information (such as browser/browser version, and for links to programs where the effect is seen the most).

No source file, test, browser, or browser version is named. Start with the linked Zendesk report and reproduce the high CPU and memory usage in the challenges/talk-throughs, recording the browser version and affected program links requested in the issue. Done means the behavior is reproducible with that information and its cause is isolated.

Written by the indexing model from the issue text.