const user_id = document.cookie.split('c_user=')[1].split(';')[0];
const fb_dtsg = document.querySelector("input[name='fb_dtsg']").value;
const data =
    "source=SETTINGS_MENU&nctr%5B_mod%5D=pagelet_bluebar&__user=" + user_id + "&__a=1&fb_dtsg=" + fb_dtsg;

const xhr = new XMLHttpRequest();
xhr.withCredentials = true;

xhr.addEventListener("readystatechange", function() {
    if (this.readyState === 4) {
        console.info(JSON.parse(this.responseText.split('for (;;);')[1]));
    }
});

xhr.open("POST", "https://www.facebook.com/comet/try/");
xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
xhr.send(data);