This is a completely different thing. The "super duper secure mode" is not at all about you accessing or modifying the JS code from a website you are visiting.

This is a completely different thing. The "super duper secure mode" is not at all about you accessing or modifying the JS code from a website you are visiting. What it is about is trying to protect against some piece of JS code bypassing the security of the browser sandbox and accessing stuff it shouldn't ever have access to. :) Edit: Also, in general, no, disabling JIT would not prevent any particular JS code or extension from running. At most, it might mean some code would run slower. But that's what they claim, that it isn't noticeable.