Hi there
The honey app works in a communicating with the server way, meaning that for each page visited on some vendor (let's say, Amazon), I would send that information to the server, and get me back some discount code. Meaning that a decent number of app logic is performed on the server side, such as scrapping the web for the CODES at the first place, sending those codes to the user, and user checks if some of them work.
That aside, the extension part is quite easy. It would require a login screen with a tracker for some websites that user visits, and that's it. The layout can be simple or elaborated with some animations.
Besides all of that, when do you plan to start the project and when is the deadline, if there is one?
Anyways, feel free to hit me up so we can talk more about this. I am very responsive. All the best