Rated 5 out of 5 stars
For me one of the most important add-ons for Firefox. I used it for years, then tried other solutions, but came back to it.
It's like a firewall, blocks all 3rd party sites, most ads and tracking scripts, which makes surfing more secure and much faster. This makes the bloated Adblock Plus/ Edge redundant (for me). Great in conjunction with NoScript, which gives the perfect security suite.
Yes, you have to do a little work to whitelist at the beginning, like NoScript. So it will probably not be for the average user, who will be stressed out. But in the end it will give you great security and a faster and less annoying web experience.