I love the concept, and would use it daily if there were features for adding/removing/viewing favorites. This is something that the official API doesn't support, so it's not something I'm faulting this application for. Impressive for sure.
Also +1 on wlqlwlql's dark-mode idea, although a color theme in general might be a better approach (but perhaps overly complicated?).
This might not be addressing your issue directly, but for my browser extension Refined Hacker News [1], once a user is logged-in in the browser site it is fairly simple to "construct" the favorite-ing endpoint URL. The URL endpoint is "/fave" and requires two query parameters: `auth` and `id`. "auth" is a random string that is unique for each story/comment and is generated from the HN server (it's required for authorization of the "favorite" request), and "id" is the story/comment's ID number.
The auth string of a story for "fave" is the same as the auth string for the "hide" and "flag" links (since they are already present, the links' hrefs contain that auth string), and so we can extract the auth string from their hrefs and use it for favoriting and un-favoriting.
The "favorite"/"follow" function is something I was also thinking about. I have some ideas about it - something like an extra feed window where only favorited (and related) things show up.
Regarding color themes - these are super easy to add.
I love the concept, and would use it daily if there were features for adding/removing/viewing favorites. This is something that the official API doesn't support, so it's not something I'm faulting this application for. Impressive for sure.
Also +1 on wlqlwlql's dark-mode idea, although a color theme in general might be a better approach (but perhaps overly complicated?).