Aren't we in an era when you literally can build your own browser with everything just you need? I have no knowledge in browsers developement. But in my field it became often easier to make your own tool\app then trying to use third party and make it work for you

My practical approach is to have a microvm for firefox and a bubblewrap “jail” for a firefox instance that runs on the host. Of course, the config options mentioned here are good too.