Chrome makes it a bit more intuitive, since the tab is called Sources, then click into Page > top > ugly-face > src.

That said, I don't understand why the author didn't simply commit the source code into the GH repo, especially since it's fully retrievable anyway. Maybe there's some goal in doing that other than security by obscurity I'm missing, since they've followed the same pattern for multiple of their repos. It seems kind of anti-collaborative to me.