External swf loaded from link doesn't work in some browsers - actionscript-3

Question

I'm developing a game that due to its extension needs to load external swf. This game is on some flash portals and loads these external swf from urlrequest and loader. Some browsers like Chrome or Opera are loading these external swf totally fine, but I'm having problems with Firefox (and I'm not totally sure if also with Microsoft Edge). ALL players that are running the game on Firefox can't load the external swf from the link (http address).
I have the "allowDomain" and "allowInsecureDomain" correctly added in both (main and external) swf files.
Which is the problem? Firefox security settings with external http addresses? Is there any way to solve it?
Any help will be appreciated!
Edit: this is the code I used:
//on the 1st frame of my main .fla
import flash.system.Security;
Security.allowDomain("*");
Security.allowInsecureDomain("*");
//on the frame I want to load the external file
var ldr:Loader = new Loader();
var bytesLoaded;
var bytesTotal;
var scene01:MovieClip;
var percentLoaded:Number = bytesLoaded/bytesTotal;
function progressListener (e:ProgressEvent):void{
trace("Downloaded " + e.bytesLoaded + " out of " + e.bytesTotal + " bytes");
percentLoaded = Math.round(percentLoaded * 100);
}
ldr.contentLoaderInfo.addEventListener(Event.COMPLETE, loadfile);
ldr.load(new URLRequest("http://img110.xooimage.com/files/e/7/e/external_file.swf"));
ldr.contentLoaderInfo.addEventListener(ProgressEvent.PROGRESS, progressListener);
function loadfile(e:Event):void {
scene01 = MovieClip(ldr.contentLoaderInfo.content);
ldr.contentLoaderInfo.removeEventListener(Event.COMPLETE, loadfile);
addChild(scene01);
scene01.gotoAndPlay(2);
}