Mozilla has launched built-in ad blocking for Firefox on iOS, according to The Verge, adding an option that can block most third-party ads and trackers before they load on an iPhone. The feature follows several weeks of testing, The Verge reports. It is built into Firefox rather than delivered through a separate extension, which matters on iOS because browser capabilities are constrained by Apple’s platform rules and WebKit-based technologies. Mozilla is using Apple’s WebKit Content Blocker technology and the EasyList filter, according to The Verge. The blocker is designed to reduce page clutter and bandwidth use by stopping many third-party ad and tracking requests before they load. The feature is not enabled by default. The Verge reports that users have to turn it on manually in Firefox for iOS under settings > browsing > ad blocker. Users can also switch it on or off for a browsing session from the site menu. Mozilla is not presenting this as a universal ad-removal system. The Verge reports that ads served directly by a website and ads shown in search results will still appear. Firefox’s own sponsored shortcuts and other sponsored content on the new-tab page will also remain visible. The launch brings Firefox for iOS closer to rival mobile browsers that already include built-in ad blocking. The Verge names Brave, Vivaldi, Opera, and others as browsers on iOS that offer similar support. Who benefits: Firefox iOS users who enable the setting get a cleaner browsing experience and may reduce bandwidth used by third-party ads and trackers. Mozilla also closes a feature gap with iOS browsers that already offer built-in ad blocking. Who's exposed: Third-party ad and tracking systems on mobile websites are most directly exposed. Sites relying on directly served ads or search-result ads are less affected based on the limitations The Verge reports.