UMatrix Style Content Blocking

[JShorthouse]

The current content-blocking system works fine, but it is an "innocent until proven guilty" system that allows all javascript unless someone else has explicitly added that domain to a filter list.

I would like to also have the option for a "guilty until proven innocent" system like umatrix that blocks all third-party javascript unless I manually allow it from a dropdown.

The implementation would not need to be as complex as umatrix, just a simple dropdown list for domains to allow/block would be sufficient, along with the ability to save the setting per-site.