Focus by Mozilla

As a solution suggests, it's a third-party ad-blocker from Mozilla for IOS. Unfortunately, compared to third-party browsers like Firefox, it is supported on Safari on IOS. Maybe it is due to some limitations on the IOS that Mozilla is not able to implement the same addon to Firefox on IOS and Apple doesn't support ad-blocking features on third-party web browsers. It does the same thing as private browsing on the desktop version of Firefox does with the same blocklist as Disconnect. Besides Adblock Plus on Safari on IOS, this is another security opportunity for your IOS device running IOS 8 and above.