Simple, lightweight, does exactly what it says Rated 5 out of 5 stars
This add-on adds semi-permanent "opt-out" cookies for major tracking ad networks. (I say "semi-permanent", because the opt-out cookies get automatically re-generated if deleted unless you uninstall the add-on, then you can delete them if you wish.)
It does not block ads, and there's no visible difference in the user interface when using it. It's extremely lightweight, requires no configuration, and stays out of the way. Truly "set it and forget it".
For those concerned with advertising networks setting long-term tracking cookies to build profiles on users, this add-on alleviates some of those risks and increases privacy. Rather than having the ad networks set those long-term cookies, this add-on ensures that the "opt-out" cookies for those networks are maintained in one's browser (even after one deletes cookies), and so prevents those networks from using cookies to identify and track users. To this end, it's excellent.