Great resource, but this website really doesn't want you going back to previous page.
I did a quick check and found that the editor is based on gfxfundamentals/live-editor, and it is doing stuff I'm not familiar with, such as injecting a blob for each editor and using some URL params hacks. I'm not sure what the issue is, but you can take a look at editor.js if you want to dig deeper.
What's certain is that you'll need to hit the back button 1 + n times (n being the number of editors on the page).
[edit] I have opened a GitHub issue for this
https://bugzilla.mozilla.org/show_bug.cgi?id=1828286
Trying to find a workaround