Browser Console, Browser toolbox tab browser #document content

The code shown on :
Browser Console Page
var newTabBrowser = gBrowser.getBrowserForTab(gBrowser.selectedTab);
newTabBrowser.addEventListener(“load”, function() {
newTabBrowser.contentDocument.body.innerHTML = “

this page has been eaten

”;
}, true);
newTabBrowser.contentDocument.location.href = “https://mozilla.org/”;

Does not work, indicating that contentDocument is null.
This is true for all pages except about:blank pages.
I want to pragramatically access all contentDocument properties from the browser console.

I understand that doing this on any https:// pages from the chrome:// window would be a security issue, I still want to do it to access and Analize live data.

How do I make this possible? I know how to compile, what lines of code should I erase to make it work?
Thank you

PD I want to add that I have made some caps security functions return true on cross domain and made nsScriptSecurityManager::CheckSameOriginURI return NS_OK, this was not enough
D