Getting information about Uploaded files - firefox-addon

Question

I am trying to write an addon for Firefox which displays the current percentage of a file being uploaded to a website (similar to how chrome does it). The problem I am having is that I have never worked with Addons for Firefox so I'm a little confused.
I have looked at the source of this Addon which was released in 2011, and this developer is referencing the following files:
Components.utils.import("resource://gre/modules/DownloadUtils.jsm");
Components.utils.import("resource://gre/modules/XPCOMUtils.jsm");
Components.utils.import("resource://gre/modules/PluralForm.jsm");
Another interesting piece of code I found when going through the source was:
Components.classes["#mozilla.org/network/http-activity-distributor;1"],
I've done a little research on these modules/classes, but I was wondering if in the last ~4 years there has been a change in the technology, and Firefox has made it a little easier to get file upload information.
I know from my experience in web development that you can use XMLHttpRequest() and addEventListener("progress", <function>, false); but is that possible with Firefox Addons? And would it work with any file uploaded to a site?
I'm pretty lost as you can see, any help would be greatly appreciated. Thank you so much!!

Answer 1

Actually it looks like all the code you need is right in that addon, i took this from that addon you posted from here: https://addons.mozilla.org/en-US/firefox/files/browse/125019/file/components/uploads.js#top
init: function() {
//dump(">>>>>>>>>>>>>>>>>>>>>> INITIALIZED\n");
// add observer
var hao = Ci.nsIHttpActivityObserver;
var _self = this;
this.observer = {
observeActivity: function(aHttpChannel, aActivityType,
aActivitySubtype, aTimestamp, aExtraSizeData, aExtraStringData) {
if ((aActivityType == hao.ACTIVITY_TYPE_SOCKET_TRANSPORT) &&
(aActivitySubtype == 0x804b0005)) { // STATUS_SENDING_TO
//dump("UPDATE STATUS: ["+aTimestamp+"] *" + aHttpChannel + "*\n");
_self.updateStatus(aHttpChannel, aTimestamp, aExtraSizeData);
}
if (aActivityType == hao.ACTIVITY_TYPE_HTTP_TRANSACTION) {
switch (aActivitySubtype) {
//case hao.ACTIVITY_SUBTYPE_RESPONSE_COMPLETE:
case hao.ACTIVITY_SUBTYPE_TRANSACTION_CLOSE:
//dump("REMOVE: *" + aHttpChannel + "*\n");
_self.removeUpload(aHttpChannel);
break;
case hao.ACTIVITY_SUBTYPE_REQUEST_HEADER:
//dump("CREATE: *" + aHttpChannel + "*\n");
_self.createUpload(aHttpChannel);
break;
}
}
}
};
Cc["#mozilla.org/network/http-activity-distributor;1"]
.getService(Ci.nsIHttpActivityDistributor)
.addObserver(this.observer);
},
shutdown: function() {
Cc["#mozilla.org/network/http-activity-distributor;1"]
.getService(Ci.nsIHttpActivityDistributor)
.removeObserver(this.observer);
},