var invocation = new XMLHttpRequest();
       invocation.open("POST", url, true);
       invocation.setRequestHeader("Content-Type", "application/json;charset=UTF-8");
       invocation.onreadystatechange = function () {
           if (this.readyState == 4 && this.status == 200)
               handler(invocation.responseText, this.status);
       }
       invocation.send(data);
   }

Hello, I have problem with Firefox when web application goes on https and there is ajax request to http. Firefox say: Cross-Origin Request Blocked: The Same Origin policy disallows reading the remote resource at http://localhost/... (Reason: CORS request did not succed). Problem is firefox doesn't send OPTION request to web api. So server part is not in game. When I change address to web api to https, firefox sends OPTION request. IE, Edge, Chrome, Opera works fine. Problem is firefox only. Why? How can I change settings to send ajax request to http when web application is on https? I cannot change web api to https! I try send request through XMLHttpRequest in javascript. I tried to set up security.fileuri.strict_origin_policy to false but nothing change. I tried to add <meta http-equiv="Content-Security-Policy" content="upgrade-insecure-requests" /> tag into page but nothing change. When I downgrade application to http it works fine. So I think there should not be problem on server side. There are following headers on server side: "Access-Control-Allow-Origin", "*" "Access-Control-Allow-Methods", "POST, OPTIONS, GET" "Access-Control-Allow-Headers", "Content-Type, Accept, Authorization, x-requested-with" There is function which is in web application: function SendData(url, data, handler) { var invocation = new XMLHttpRequest(); invocation.open("POST", url, true); invocation.setRequestHeader("Content-Type", "application/json;charset=UTF-8"); invocation.onreadystatechange = function () { if (this.readyState == 4 && this.status == 200) handler(invocation.responseText, this.status); } invocation.send(data); } I need help to solve this problem to send ajax request from https web application into http web api. Thank you.