UserScript - XHR Interceptor

gistfile1.js

function Interceptor(nativeOpenWrapper, nativeSendWrapper) {
	XMLHttpRequest.prototype.open = function () {
		// Code here to intercept XHR
		return nativeOpenWrapper.apply(this, arguments);
	}
	XMLHttpRequest.prototype.send = function () {
		this.onloadend = function() {
			if(this.capture) {
				console.log(this.responseText);
			}
		}
		return nativeSendWrapper.apply(this, arguments);
	}
}

//	Injects the code via a dynamic script tag

var script = document.createElement("script");
script.type = "text/javascript";
script.textContent = "(" + Interceptor + ")(XMLHttpRequest.prototype.open, XMLHttpRequest.prototype.send);";

document.documentElement.appendChild(script);
document.documentElement.removeChild(script);