What is the general nature of your idea? If it’s just about the UI or something high-level, then I’d recommend finding a program language you feel comfortable with, and a library for that language that includes browser functions.
For me, for example, I would choose C++, and the C++ framework OpenFrameworks, which includes functions that would in theory let me display a browser display for a URL, and develop the rest of the UI. Assuming that works well enough, and does the parts I don’t want to do, I could probably make a web browser this way, that might serve whatever my needs/desires were for the project.
It wouldn’t be likely to be enough to compete as a general-purpose browser product with something like Opera or Vivaldi, let alone Firefox, but it might well serve a specific need/desire far better than those would.