It would be nice if we had browsers that were actually user-agents that allow full pluggable customizability for all cookie, header, UI, request, and history behavior. Then, this would just be a plugin that anyone could install.
And then people install garbage extensions that break the browser and people think "Wow, this firefox browser is so buggy and slow" and switch to chrome. And then your extensions break with every single browser update because they are tampering with internal code.
Everyone is free to fork a browser and apply any changes they want. Allowing extensions to change anything at all essentially is the same as forking and merging your changes with upstream every update.
