That one uses WebKit. I wonder if anybody actually got Gecko to run on iOS. As I understand, there are "only" two problems - Apple not allowing other HTML/JS implementations, and Apple not allowing writable, executable memory. I don't know what the status of the first is, but you can get around the latter by just using an interpreter instead of a JIT (which is of course terribly slow).

Or, you decide Apple is never going to let your engine on the App store, and then you just include the JIT. The enforcement is done at time of submission to the app store, not at runtime. IIRC, you can just call a certain function to mark a memory region as writable or executable, but Apple detects this call statically.

I further wonder if you could just distribute binaries, outside of the app store, and your users would have $99 developer accounts, and run a little script to "build their project with XCode", signing and installing it to their device?

It uses WebKit rather than Gecko due to the appstore restrictions though