I run uMatrix too and I agree it gets annoying at times (and it gives you first-hand insight into how rotten the web industry is). That said, pretty much all the stuff from your comment upthread are things 99% of websites have no business accessing. So an uMatrix-like (default-deny) control for permissions should work well IMO, with only occasional cases when you need to whitelist something.
I'm also thinking about another kind of plugin - one that simply monitors access to browser API calls required to get information like resolution, mouse pointer position, battery level, etc. and that would display you only the "spying level" of a site as an icon. Like the padlock icon, changing colors from green to yellow to red or something, and that would expand when clicked to show something like this:
Spying level: MODERATE.
This website has accessed following information about your system:
- screen resolution - 256 requests
- mouse pointer position - 8192 requests
- location - 42 requests
- battery level - 16 requests
[CLICK] to send an e-mail to webmaster (webmaster@example.com) asking for
information about how they're using your data.
I'm not sure if current plugin infrastructure has enough power to hook JS APIs like that though.