New in Safari for iOS 9 and El Capitan is a content blocker-specific extension.
Well, reader, there’s a good reason for introducing a new extension point. Benjamin Poulain writes on the WebKit blog:
It is an area were we want to do better. We are working on new tools to enable content blocking at a fraction of the cost.
A while back, I was going to post this article about how AdBlock slows down your browser because it iterates through all the iframes on a page, running on each of them. I ultimately didn’t link to it because I think the author missed the point of why most people block ads: not because they’re slow, but just because they don’t want to see ads.
But I thought of it again after I heard about content blockers baked into Safari. I don’t use AdBlock, but I do use Steven Frank’s excellent ShutUp.css. The internet is much more peaceful without comments, but I also see a small performance hit on most modern web pages because of the number of iframes they contain.