I'm not talking about the sandboxed browser being able to "clear your hard drive", etc. I'm talking about users having no real agency when it comes to controlling the presentation of websites. (Sure, it's code running on your computer. You're free to attach a debugger to step thru native code that runs a VM that runs a nested VM that's ultimately running the code you'd actually like to influence. Let me know how that goes for you.)
Have you seen JSLinux[1]?