Active Choice Interventions at Scale: Browser Defaults under the Digital Markets Act

Can active choice mitigate preset-default effects? Using difference-in-differences around the EU Digital Markets Act’s choice-screen mandate, we study Firefox on iOS and Android. From month 15 onward, Firefox usage was 91 percent higher on iOS and 13 percent higher on Android relative to a no-mandate counterfactual. The platform gap is consistent with rollout differences: iOS reached existing users, while Android primarily reached new devices. Market-share data corroborate movement away from defaults: Safari declined on iOS, with gains concentrated in Chrome; Firefox’s smaller gains were meaningful relative to baseline. Chrome declined on Android, where it was default, and Firefox rose modestly.