I enjoy the challenges, however, I find it really frustrating when I lose my work every-time I accidentally navigate back to the previous page. This happens easily with a Macbook Pro's trackpad. This heavily detracts from usability and prevents me from 'wanting to complete' the rest of the challenges.

I recommend two modifications:

1) Disable Navigating Forwards/Backwards in the browser, like Jupyter Notebook

2) Make use of HTML5's localstorage / HTML Web Storage for each challenge.