Mark Mayo, Mozilla CEO and chief manager of Firefox, has introduced project Tofino. In that project, there are a number of GUI experiments for a web browser which Mozilla is working on. Firefox development is not going to be affected but it's a fact that Firefox usage has been going down steadily. It is interesting that the whole project is built on top of a Chromium-based engine Electron, created by GitHub for Atom editor. Instead of XUL used in Mozilla, the browser's user interface is created using React.