Firefox

The Register has learned from those involved in the browser trade that Apple has limited the development and testing of third-party browser engines to devices physically located in the EU. That requirement adds an additional barrier to anyone planning to develop and support a browser with an alternative engine in the EU.

It effectively geofences the development team. Browser-makers whose dev teams are located in the US will only be able to work on simulators. While some testing can be done in a simulator, there's no substitute for testing on device – which means developers will have to work within Apple's prescribed geographical boundary.

... as Mozilla put it – to make it "as painful as possible for others to provide competitive alternatives to Safari."