It's your responsibility to download, install and run the appropriate proxy server. If that's outside your comfort zone, don't. See
https://github.com/JimmXinu/FanFicFa.../ProxyFeatures
If
open_pages_in_browser:true isn't working, is the Chrome who's cache you configured not your default browser? It needs to be for
open_pages_in_browser:true
Honestly, if you are a new user just coming to FFF for the first time and only care about ffnet, I'd use a different tool such as
WebToEpub,
Fanfictiondownloader, or ffnet's own mobile app.
Downloading from ffnet is a pain now and if it wasn't one of the biggest fanfic sites around with 20+ years of stories, I wouldn't support it anymore.