Firefox for iOS cannot block ads like desktop Firefox because Apple requires all iOS browsers to use WebKit (App Store Review Guideline 2.5.6), preventing third-party engines like Gecko. Instead, Firefox relies on Apple's Content Blocker API introduced in iOS 9 (2015). Content blockers use declarative JSON rules rather than running code per request, enhancing privacy since the blocker never sees browsing history.

Compatible apps include 1Blocker, Ad Guard, Wipr, and Ad Block Plus. Rules are compiled ahead of time by WebKit, applying triggers (domain, resource type, URL regex) with actions (block, hide via CSS, block cookies). Since iOS 17.4 (2024), the EU's Digital Markets Act allows alternative engines in the EU, but Firefox hasn't fully migrated.

Activation requires enabling in iOS Settings, then selecting in Firefox. Multiple blockers can run simultaneously, though overlapping rules may break site layouts. Firefox Focus offers built-in tracking protection without extensions.