I am almost at an advanced level in Python and JavaScript, and planning on going to c++/rust.

I had an idea of creating a web browser using an existing browser engine: gecko in this case.

I don’t want to touch any of the engine parts of the code, I want to mainly focus on the UI, removing useless features, and adding my own features that are created using C++.

The main question is, how? Should I clone the Firefox code from Mercurial and just update the code of the UI and add my own features using C++ or I just build the UI part and there is a way to merge the browser engine to the UI?

Sorry if the question is not up to the standards.

I tried learning C++/Rust but I am not sure which one to use. Or should I use both?