I've been doing something similar for years, though the implementation method has changed some as my preferred browser and the set of available extensions has shifted. I want to browse the web with a white-list approach to which pages are allowed to display elements that are anchored to screen coordinates rather than scrolling with the page. Generally speaking, the only pages that should be permitted to pin an element in front of the main content are web apps, but most of the pages I visit are (or should be) purely document-oriented.