function downloadFile(httpLoc) {
    try {
        //new obj_URI object

        var obj_URI = Components.classes["@mozilla.org/network/io-service;1"].getService(Components.interfaces.nsIIOService).newURI(httpLoc, null, null);
        //new file object
        var obj_TargetFile = Components.classes["@mozilla.org/file/local;1"].createInstance(Components.interfaces.nsILocalFile);
        //set file with path
        obj_TargetFile.initWithPath("c:\\atemp\\logo_beta.png");
        //if file doesn't exist, create
        if (!obj_TargetFile.exists()) {
            obj_TargetFile.create(0x00, 0644);
        }
        //new persitence object
        var obj_Persist = Components.classes["@mozilla.org/embedding/browser/nsWebBrowserPersist;1"].createInstance(Components.interfaces.nsIWebBrowserPersist);

        // with persist flags if desired
        const nsIWBP = Components.interfaces.nsIWebBrowserPersist;
        const flags = nsIWBP.PERSIST_FLAGS_REPLACE_EXISTING_FILES;
        obj_Persist.persistFlags = flags | nsIWBP.PERSIST_FLAGS_FROM_CACHE;


        //save file to target
        obj_Persist.saveURI(obj_URI, null, null, null, null, obj_TargetFile);
    } catch (e) {
        //alert('errosr is '+'\n'+e);
    }
}