You are thinking of SpiderNode, and/or NodeMonkey. Other than the principals leaving Mozilla for Facebook, this work was superseded by Tim Caswell's Luvmonkey:
Turns out Node is really well factored, so emulating the V8 API on top of SpiderMonkey, especially back in 2011 as the Spider-Node-Monkey project tried, is harder. It's the "long way 'round".
Binding libuv to any engine that implements ES5+ is easier and gives Node interop.
As for XULRunner, sorry -- no leverage. If you see some, make it a business and show us up.
https://github.com/creationix/luvmonkey
Turns out Node is really well factored, so emulating the V8 API on top of SpiderMonkey, especially back in 2011 as the Spider-Node-Monkey project tried, is harder. It's the "long way 'round".
Binding libuv to any engine that implements ES5+ is easier and gives Node interop.
As for XULRunner, sorry -- no leverage. If you see some, make it a business and show us up.