_ff-addon-snippet-LoadContextAndGoodies - Gets the nsILoadContext from nsIRequest. Also returns some common stuff like nsIDOMWindow, contentWindow, gBrowser, tab, and browser.

_ff-addon-snippet-LoadContextAndGoodies.js

function loadContextAndGoodies(request, return_goodies) {
  var loadContext = null;
  
  if (request instanceof Ci.nsIRequest) {
      try {
          if (request.loadGroup && request.loadGroup.notificationCallbacks) {
              loadContext = request.loadGroup.notificationCallbacks.getInterface(Ci.nsILoadContext);
          }
      } catch (ex) {
        console.exception('request loadGroup with notificationCallbacks but oculd not get nsIloadContext', ex);
      }
      if (!loadContext) {
        try {
            if (request.notificationCallbacks) {
                loadContext = request.notificationCallbacks.getInterface(Ci.nsILoadContext);
            }
        } catch (ex) {
          console.exception('request has notificationCallbacks but could not get nsILoadContext', ex);
          /* start - noit's backup try, it might be redundant (im not sure) as Wladamir Palant didn't have this way*/
          try {
            var interfaceRequestor = httpChannel.notificationCallbacks.QueryInterface(Ci.nsIInterfaceRequestor);
            loadContext = interfaceRequestor.getInterface(Ci.nsILoadContext);
          } catch (ex) {
            console.exception('backup method failed:' ex);
          }
          /* end - my backup try, it might be redundant as Wladamir Palant didn't have this way*/
        }
      }
  } else {
    console.warn('request argument is not instance of nsIRequest')
  }
  
  if (return_goodies) {
    if (!loadContext) {
      return null;
    }
    
    var contentWindow = loadContext.associatedWindow;
    var DOMWindow = contentWindow.top.QueryInterface(Ci.nsIInterfaceRequestor)
                                     .getInterface(Ci.nsIWebNavigation)
                                     .QueryInterface(Ci.nsIDocShellTreeItem)
                                     .rootTreeItem
                                     .QueryInterface(Ci.nsIInterfaceRequestor)
                                     .getInterface(Ci.nsIDOMWindow);
    var gBrowser = DOMWindow.gBrowser;
    if (gBrowser) {
      var tab = gBrowser._getTabForContentWindow(contentWindow.top);
      var browser = tab.linkedBrowser;
    } else {
      var tab, browser = null;
    }
    var goodies = {
      loadContext: loadContext,
      DOMWindow: DOMWindow,
      gBrowser: gBrowser,
      contentWindow: contentWindow,
      browser: browser,
      tab: tab
    };
    
    return goodies;
  } else {
    return loadContext;
  }
}

README

Rev1

• Based on:
  • StackOverflow :: Is it possible to know the target DOMWindow for an HTTPRequest?
    • To get the nsILoadContext
  • StackOverflow :: Finding the tab associated with a DOM window
    • To get the nsIDOMWindow from loadContext.associatedWindow (which is a contentWindow)
  • StackOverflow :: How can I change the User Agent in just one tab of Firefox?
    • This is code I put togather, and for reason I had this method where I would get var interfaceRequestor, I implemented this above as a backup as it might be redundant.

Nice way to detect if in private mode:

isRequestFromPrivateWindow: function (subject, httpChannel) {
        "use strict";
        var loadContext, interfaceRequestor, isPrivate = false, contentWindow;
        try {
            interfaceRequestor = httpChannel.notificationCallbacks.QueryInterface(Components.interfaces.nsIInterfaceRequestor);
            try {
                loadContext = interfaceRequestor.getInterface(Components.interfaces.nsILoadContext);
            } catch (ex) {              
                try {
                    loadContext = subject.loadGroup.notificationCallbacks.getInterface(Components.interfaces.nsILoadContext);
                } catch (ex1) {}
            }
            if (loadContext) {              
                isPrivate = loadContext.usePrivateBrowsing;
            }
        } catch (ex2) {}
        return isPrivate;
    }

From https://pastebin.mozilla.org/8823253 by user @Devuct off of IRC #extdev

https://gist.github.com/intika/503ab65f457dc20bb77b/revisions

Just fixed a little bug... we could have a request without tab resulting in tab being null
(DOMWindow.gBrowser exist but not tab for some requests)

Way cool @intika thanks for that catch. I had to update your catch though:

if (gBrowser && gBrowser._getTabForContentWindow(contentWindow.top)) {

cuz if gBrowser is undefined or null then doing gBrowser.anything will cuase error :)

yeah that was my first edit i thought it was not necessary to make both tests :)

Possibly better version:

function getLoadContext(request) {
    var loadContext = null;

    if (request instanceof Ci.nsIRequest) {
        try {
            if (request.loadGroup && request.loadGroup.notificationCallbacks) {
                loadContext = request.loadGroup.notificationCallbacks.getInterface(Ci.nsILoadContext);
            }
        } catch (ex) {
            console.exception('request loadGroup with notificationCallbacks but oculd not get nsIloadContext', ex);
            try {
                if (request.notificationCallbacks) {
                    loadContext = request.notificationCallbacks.getInterface(Ci.nsILoadContext);
                }
            } catch (ex) {
                console.exception('request has notificationCallbacks but could not get nsILoadContext', ex);
                /* start - noit's backup try, it might be redundant (im not sure) as Wladamir Palant didn't have this way*/
                try {
                    var interfaceRequestor = httpChannel.notificationCallbacks.QueryInterface(Ci.nsIInterfaceRequestor);
                    loadContext = interfaceRequestor.getInterface(Ci.nsILoadContext);
                } catch (ex) {
                    console.exception('backup method failed:', ex); // fixed on aug 14 2015
                }
                /* end - my backup try, it might be redundant as Wladamir Palant didn't have this way*/
            }
        }
    } else {
        console.warn('request argument is not instance of nsIRequest')
    }

    return loadContext;
}