Safari and anything using the Safari View Controller. Which is, admittedly, a bit limited to use for a full custom browser.<p>The faster JS engine was also limited to Safari for a few iOS versions before it was extended to third-party applications, so perhaps they&#x27;re taking the same approach here.<p>It&#x27;s worth noting that they could also integrate their own ad blocking into their custom browser, which other third-party iOS browsers have been doing for years.