Firefox on iOS: The WebKit Mandate and EU DMA Impact

For years, Apple’s strict App Store policies have forced all third-party web browsers on iOS, including Mozilla's Firefox, to run on Apple’s own WebKit rendering engine rather than their native engines. While Apple claims this restriction protects user security and device performance, critics argue it stifles competition and makes every iOS browser a reskinned version of Safari. Recently, the European Union's Digital Markets Act (DMA) forced Apple to drop this requirement, allowing Mozilla to use its proprietary Gecko engine on iOS. However, because Apple limited this rule change strictly to the EU, browser developers now face the costly burden of maintaining two entirely different iOS apps.

The App Store Policy: Why Firefox Uses WebKit

Under Apple’s historical App Store Review Guidelines (specifically Guideline 2.5.6), all apps that browse the web must use the appropriate WebKit framework and WebKit JavaScript.

On desktop and Android devices, Firefox runs on Gecko, a browser engine developed by Mozilla. Gecko dictates how web pages are rendered, how fast the browser operates, and what features—such as advanced privacy tools and browser extensions—are supported. Because of Apple's mandate, Mozilla was forbidden from bringing Gecko to the iPhone and iPad. To exist on the App Store, Firefox had to be built on top of WebKit, the same engine that powers Apple's Safari.

Consequently, Firefox on iOS could only offer a customized user interface and basic account syncing. It could not import its unique security architecture, rendering speeds, or full library of add-ons.

Apple's Justification vs. Mozilla's Reality

Apple has consistently defended the WebKit mandate by citing security, privacy, and battery life. Because WebKit is deeply integrated into iOS, Apple argues that having a single browser engine allows them to quickly deploy security patches across the entire operating system whenever a web vulnerability is discovered. Furthermore, Apple states that WebKit is uniquely optimized for Apple Silicon, preventing poorly coded third-party engines from draining user batteries.

Mozilla and other competitors view the mandate as an anti-competitive roadblock. By forcing all browsers to use WebKit, Apple ensures that no rival browser can outperform Safari in speed or web-standard compatibility. Furthermore, if WebKit has a bug or lacks support for a specific web application feature, every single browser on iOS suffers from that exact same limitation, preventing Mozilla from fixing issues independently for its users.

How the EU DMA Changed the Rules

In March 2024, the European Union’s Digital Markets Act (DMA) went into full effect. The DMA is a piece of legislation designed to curb the market power of tech "gatekeepers" and promote fair competition.

Under the DMA, Apple is legally prohibited from forcing developers to use its proprietary software engines. To comply with the law, Apple released iOS 17.4, which officially lifted the WebKit restriction. For the first time, Apple introduced APIs and frameworks that allow third-party developers like Mozilla to build iOS browsers using their own engines, opening the door for a Gecko-powered Firefox on the iPhone.

The Catch: A Fragmented Ecosystem

While the DMA technically gives Mozilla the freedom to use Gecko, Apple’s specific method of compliance has created a new problem. Apple decided to lift the WebKit ban only for users physically located within the 27-nation European Union, keeping the restriction firmly in place for the rest of the world.

Furthermore, Apple requires developers wishing to use alternative engines in the EU to agree to new business terms. These terms include a "Core Technology Fee" of €0.50 for each annual app install over one million—a fee that could financially penalize free apps like Firefox.

Because of Apple's geographical restriction, Mozilla cannot simply replace its existing iOS app with a Gecko-based version. Instead, Mozilla is forced to maintain and update two completely separate versions of Firefox for iOS: a WebKit version for the global market and a Gecko version exclusively for the EU. For a non-profit-backed organization like Mozilla, this requirement demands double the engineering resources, effectively neutralizing much of the competitive relief the DMA intended to provide.