In case you were already familiar with Narcissus, this appears to just be Narcissus packaged in a Firefox addon, not a new JavaScript implementation written in JavaScript as the title implies.
You're correct. To me, JavaScript in JavaScript that can run in the browser was the most important part (although I should have added "in the browser"). If I had called it "Zaphod - run Narcissus in firefox", it probably wouldn't have gotten anyone's attention.
This is one of the main goals of Narcissus and Zaphod, actually, since it's much easier to hack Narcissus than SpiderMonkey. We're working on integrating Harmony proposals into Narcissus.
Sorry, can someone please give an overview of what this is and how it works (I did not find any detailed examples on the site).
My understanding is that its an alternative javascript engine that can be modified (using javascript itself I assume) and those modifications packaged and shared.
Is that right? I was looking for an example of how you modify the engine and what can be modified. Any ideas?
So, when if I install this extension, I can hack those files (in the extension's directory I assume) reload the browser and the javascript engine will do whatever I have changed?