There is a sandbox, but to be a competitive third-party browser you also need something else: Safari has a special permission (entitlement) that allows it to c

There is a sandbox, but to be a competitive third-party browser you also need something else: Safari has a special permission (entitlement) that allows it to compile JavaScript to native code. This is what their JIT does. This is something that no third-party app has ever gotten. No JIT means slow JavaScript. No ASM.js, no WebAssembly. I have mixed feelings about giving third-party applications (browsers) this permission. Bugs can lead to remote code execution, can lead to sandbox escapes, can lead to compromised devices. This is a really tough one. Specially for apps that load random content from the web.