Error receive access token with browser different IE

Hi,

i have a problem when i use a browser different to Internet Explorer for receiving access_token.

In firefox i have this error:

Error: No access token was found for element. You must specify an access token directly on the element using attribute 'powerbi-access-token' or specify a global token at: powerbi.accessToken.

this is code:

 var access_token="";

 var settings = {
   async: true,
   crossDomain: true,
   url: "https://login.windows.net/common/oauth2/token",
   method: "POST",
   data: "request "
   dataType: "json"
 }

 $.ajax(settings).always(function (response) {
  access_token=response.access_token;