How to identify who initiated the http request in firefox?

I am developing a new Firefox addon that intercept all Firefox's network traffic (http(s) requests with http-on-modify-request)

With my current code, I am able to separate requests coming from web-pages/tabs and all the other components (RSS feed updates, XHR requests from XPCOM components, extensions, extensions manager, etc.)

I would like to identify who initiate a request other than the tab's traffic with precision not just the whole group? (RSS, XPCOM components, extensions, extensions manager, etc)

Example: a hypothetical custom variable requestRequestor would have a value to identify a specific addon or RSS update etc.

I found this similar question without a a solution.

Current code to identify the whole group (getting the browser that fires the http-on-modify-request notification) is:

Services.obs.addObserver(httpObs, 'http-on-modify-request', false);
//Services.obs.removeObserver(httpObs, 'http-on-modify-request'); //uncomment this line, or run this line when you want to remove the observer

var httpObs = {
    observe: function (aSubject, aTopic, aData) {
        if (aTopic == 'http-on-modify-request') {
            /*start - do not edit here*/
            var oHttp = aSubject.QueryInterface(Components.interfaces.nsIHttpChannel); //i used nsIHttpChannel but i guess you can use nsIChannel, im not sure why though
            var interfaceRequestor = oHttp.notificationCallbacks.QueryInterface(Components.interfaces.nsIInterfaceRequestor);
            //var DOMWindow = interfaceRequestor.getInterface(Components.interfaces.nsIDOMWindow); //not to be done anymore because: //instead do the loadContext stuff below
            var loadContext;
            try {
                loadContext = interfaceRequestor.getInterface(Components.interfaces.nsILoadContext);
            } catch (ex) {
                try {
                    loadContext = aSubject.loadGroup.notificationCallbacks.getInterface(Components.interfaces.nsILoadContext);
                    //in ff26 aSubject.loadGroup.notificationCallbacks was null for me, i couldnt find a situation where it wasnt null, but whenever this was null, and i knew a loadContext is supposed to be there, i found that "interfaceRequestor.getInterface(Components.interfaces.nsILoadContext);" worked fine, so im thinking in ff26 it doesnt use aSubject.loadGroup.notificationCallbacks anymore, but im not sure
                } catch (ex2) {
                    loadContext = null;
                    //this is a problem i dont know why it would get here
            /*end do not edit here*/
            /*start - do all your edits below here*/
            var url = oHttp.URI.spec; //can get url without needing loadContext
            if (loadContext) {
                var contentWindow = loadContext.associatedWindow; //this is the HTML window of the page that just loaded
                //aDOMWindow this is the firefox window holding the tab
                var aDOMWindow =;
                var gBrowser = aDOMWindow.gBrowser; //this is the gBrowser object of the firefox window this tab is in
                var aTab = gBrowser._getTabForContentWindow(; //this is the clickable tab xul element, the one found in the tab strip of the firefox window, aTab.linkedBrowser is same as browser var above //can stylize tab like = 'blue'; //can stylize the tab like = 'red';
                var browser = aTab.linkedBrowser; //this is the browser within the tab //this is what the example in the previous section gives
                //end getting other useful stuff
            } else {
                Components.utils.reportError('EXCEPTION: Load Context Not Found!!');
                //this is likely no big deal as the channel proably has no associated window, ie: the channel was loading some resource. but if its an ajax call you may end up here

As of June 2020, there is no official method/way of achieving http request requester filtering/identification.

Currently the only possibility is what is done on the question's code which is separating requests from web-pages/tabs and the other Firefox's components (feed updates, extensions requests, XHR requests from XPCOM components, etc).

As mentioned on the comments this is an internal limitation of Firefox. The current Firefox's core code does not implement a requester tracking and thus does not know who initiated the request and why. It may be useful to know that Chrome dev tools got recently this feature.