Are you using macOS? If so, those keybindings work everywhere.
As far as I can tell, Hacker News doesn't impose any custom keybindings (the client-side scripting on this site[0] is very simple).
[0]: https://hackertimes.com/hn.js
gsettings set org.gnome.desktop.interface gtk-key-theme "Emacs"
Are you using macOS? If so, those keybindings work everywhere.
As far as I can tell, Hacker News doesn't impose any custom keybindings (the client-side scripting on this site[0] is very simple).
[0]: https://hackertimes.com/hn.js