Rated 5 out of 5 stars
this is and works great !
one request: it would be GREAT if this could - in addition to the site's css - scan css applied by stylish. If that's too hard to implement you could also simply provide the option to manually select a css file for a page that you then have your extension scan for coverage. This would be very useful for designing userstyles for pages. (like the page gets updated and thus many rules are obsolete etc)