It works very well on most sites but on Facebook it has unintended side effects. I use it to block annoying features that Facebook has implemented without user input, but it seems that they've foreseen this and implemented multiple replacements of the same features. This makes it so that I have to block up to a couple dozen of the same feature before I find it completely blocked. When this happens though I find that doing so has caused other features that don't seem to be related to fail to appear on their page. Because of this side effect, I'm subtracting three stars from the overall rating. If you can come up with a way to effectively block specific features on Facebook without side effects, I'll move my rating up accordingly.