Great add-on, would definitely recommend to anyone. You can customize it to block ads on certain websites (I have it set to block ads on YouTube only, due to too many ads.) And you can also blacklist low-quality websites you don't want to visit.

For example, I have it set to block access to ||www.usatoday.com
||www.washingtonpost.com
Now, why you may ask? Well they gave me a popup to disable firefox's anti-tracking protection in order to continue to their site. So I said screw that, you're getting blacklisted! And now, anytime I try to visit those website's, uBlock origin prevents me from visiting :)