first_session_attribute.js

// Place this clode below the Optimizely snippet

var first_session = window.optimizely.get('visitor').first_session
if (first_session == true) {
  first_session = "true";
} else if (first_session == false) {
  first_session = "false";
}

window.optimizely = window.optimizely || [];
window.optimizely.push({
  "type": "user",
  "attributes": {
    "first_session": first_session
  }
});