browser extension to replace JavaScript file on a live site for testing

Question

I'm looking for a browser extension (Firefox, Chrome) allowing to replace a Javascript file on a live Web site to do some testing/hacking.

Basically, it should take a URL and load another one instead (locally or on a HTTP development server).

Any idea?

Answer 1

I think this is a task for a personal proxy. You can sniff traffic on the proxy and apply rules to modify requests/content