https://www3.otava.fi/demo/forum_2_digikirja/

This site is a digital book and i want to download it to have it for offline
use, since i am traveling and need to study at the same time. The site itself
gets downloaded but it will not load the other branches of the site and has
only the "loading circle" spinning there forever and then it says in red that
"no internet connection". I've tried with every action option. Any help?