There's a new ad-blocker coming to the app store. Today, Mozilla is launching Focus, a new program taking advantage of iOS 9's content-blocking API. Unlike broader blockers like Crystal or Peace, Focus is designed to give the user in-depth control over what to block from a given page, with different settings to block ads, analytics, and tracking through social networks like Facebook.

The app borrows its blacklist from Disconnect.me, a browser plug-in that maintains a list of 5000 trackers, including many associated with ad networks. The app will also identify new trackers on the fly, using heuristics to identify any content following a user from site to site. Focus will only work with Safari because of the way iOS manages content blockers, but Mozilla is hoping Apple will open the system up in the months to come, allowing users to combine Focus with Firefox.

Still, the new app is a remarkable move for a company that has steadfastly opposed tracking while advocating for the open web. Mozilla was a leading advocate for Do Not Track standards, and has consistently criticized the proliferation of trackers on the web. At the same time, ad-blockers have also been criticized for pushing publishers to less open platforms run by Apple and Facebook. In September, developer Marco Arment pulled his ad-blocker from the App Store after tens of thousands of sales, stating that it "just didn't feel right."