Or it's a anti-competitive move disguised as a "avoid vulnerabilities" but in reality they just really want to make sure iOS users keep using the one and only browser (Safari).

You can if it’s for educational purposes.

That's the part Apple is not allowing in third party apps.

Not outside of JavaScriptCore they don’t.

Thus one cannot make a JIT compiler for js and thus pages are slow.

Game engines such as Unity use il2cpp to go from the C# stuff into C++ that can be statically compiled as running the C# as bytecode would be too slow without a jitter.

The interface between SpiderMonkey and the rest of Firefox is here: https://searchfox.org/mozilla-central/source/js/src/jsapi.h.

Nitpick: you can but you cannot ship it via the App Store.

> Thus one cannot make a JIT compiler for js and thus pages are slow.

Lack of JIT doesn't slow down pages much. I believe the difference is so small that it might even be possible to be faster without JIT for most pages, especially on low power devices, it's only computation heavy pages that are going to suffer and even then it's not like you can't optimize common patterns statically ahead of time.

It doesn't mean that it's a good idea to invest into it, you are still under Apple's mercy and they clearly don't want competing browser engines.

So why do you think so many major companies invest such a huge amount of money in JS JITs? Google, Apple, Microsoft, Oracle, Mozilla all maintain JS JITs and spend what I guess is hundreds of millions of dollars a year on it.

> let's not weaken the argument by indulging a penchant for hyperbole

Please don’t be so dismissive and snide - there’s no need for that.

Then your initial estimate was way off, because you were suggesting multiple hundreds of millions and the average salary probably isn't that high.

> there’s no need for that

Honest argument wouldn't require such forceful correction.

> Honest argument wouldn't require such forceful correction.

Please try to tone it down.

You can't ship a native JIT (execute native code from the heap), I think it's enforced automatically by the App Store. So shipping your own JavaScript engine is out.

You can't download and interpret third-party code, I think this is enforced by human reviews, so shipping your own Web rendering stack is out.

You can use your own network stack with WebKit on top, which would let you offer some value to users like more advanced ad/tracker blocking.

Mozilla ported the true Firefox to iOS many, many years ago and Apple just rejected it from the store.