This is an extraordinary add-on. I found it to be very intuitive -- there was almost no learning curve. It allows granular control over what web sites may and may not access. It's sad, scary, and wrong how many external sites are referenced by web sites that you visit -- and if any of those sites have been compromised, your computer is likely next. uMatrix provides a simple and effective protection against Internet threats, and as a bonus, helps reduce tracking while speeding up your browsing.