Firefox is one of a few applications that still has pretty decent customization options, especially if you can get into editing some CSS. They should find a way

Firefox is one of a few applications that still has pretty decent customization options, especially if you can get into editing some CSS. They should find a way to work them into convenient UI, so other, less tech savvy users, or just users who don't have time to tinker with config files, could easily customize their browsing experience. It is sad, that in this day and age of various display sizes (4K, widescreen) and scaling (not only retina 2x screens, but 125% scaling on Windows too) Firefox designers are still working with pixels. How about using some of that modern CSS magic and building truly responsive UI, that works not only for desktops, but tablets and phones (e.g. Pinephone)?