Earlier quoted context omitted.
There're some extra features (e.g. bookmarks) that utilize scripting and data storing. So a userstyle wouldn't cut it. A user script though would. Also privacy-wise I think there isn't a way to limit an extension to a single site, something possible with a user script.
> Also privacy-wise I think there isn't a way to limit an extension to a single site On Chrome/Edge you can, not sure about Firefox. Additionally this extension only even asks for permission to access Hacker News and some backend stuff presumably used for the paid tier.
Yes, you're right on asking permissions. I didn't had a site-specific extension so couldn't see them. Unfortunately restricting any extension, if it doesn't restrict itself, is only possible on Chrome and its derivatives.