Inappropriate ads, gone. Trackers, gone. Websites, working.* The best of the best multi-purpose blockers I've found.

*except in rare cases, in which Ublock is easily disabled.

The only negative is that it saves the websites you added a blocked element to on your offline filter list as comments.

Must have browser extension.

The best add-on ever! I mean, It blocks EVERYTHING, it's FREE SOFTWARE (GPLv3), and fun fact, it works better on Firefox than on Chrome! Thank you @gorhill and thanks to all the devs involved on this magnificent open source software <3