Many to Many relationship from Marketinglist to Marketinglistmembers is not working ?

I am using "AddListMembersList" Request for adding contacts to one marketing list(marketinglist members to marketinglist). when i am using  "XrmSvcToolkit.execute"  method it is working fine for IE and chrome. But while running in mozilafirefox this request was not working properly. 

While debugging i am getting problem in doSoapRequest function.

In this function this line was not executing. "req.open("POST", serverUrl + soapEndpoint, async);"

Below is the code what i am executing.

var requestMain = ""

            requestMain += "    <Execute xmlns=\"http://schemas.microsoft.com/xrm/2011/Contracts/Services\" xmlns:i=\"http://www.w3.org/2001/XMLSchema-instance\">";
            requestMain += "      <request i:type=\"b:AddMemberListRequest\" xmlns:a=\"http://schemas.microsoft.com/xrm/2011/Contracts\" xmlns:b=\"http://schemas.microsoft.com/crm/2011/Contracts\">";
            requestMain += "        <a:Parameters xmlns:c=\"http://schemas.datacontract.org/2004/07/System.Collections.Generic\">";
            requestMain += "          <a:KeyValuePairOfstringanyType>";
            requestMain += "            <c:key>ListId</c:key>";
            requestMain += "            <c:value i:type=\"d:guid\" xmlns:d=\"http://schemas.microsoft.com/2003/10/Serialization/\">" + listId +"</c:value>";
            requestMain += "          </a:KeyValuePairOfstringanyType>";
            requestMain += "          <a:KeyValuePairOfstringanyType>";
            requestMain += "            <c:key>MemberIds</c:key>";
            requestMain += "            <c:value i:type=\"d:ArrayOfguid\" xmlns:d=\"http://schemas.microsoft.com/2003/10/Serialization/Arrays\">";
            for (var i = 0; i < contactId.length; i++) {
                requestMain += "              <d:guid>" + contactId[i] + "</d:guid>";
            }
            requestMain += "            </c:value>";
            requestMain += "          </a:KeyValuePairOfstringanyType>";
            requestMain += "        </a:Parameters>";
            requestMain += "        <a:RequestId i:nil=\"true\" />";
            requestMain += "        <a:RequestName>AddListMembersList</a:RequestName>";
            requestMain += "      </request>";
            requestMain += "    </Execute>";

            XrmSvcToolkit.execute({ executeXml: requestMain, async: false, successCallback: succss_N, errorCallback: error_N });

If anyone find the solution please let me know.

Thanks in advance.

J.sravan