Two Ajax requests with one open() method?

So as I was following the instructions in the video, I wrote the following code:

    var xhr = new XMLHttpRequest();
    xhr.onreadystatechange = function() {
      if (xhr.readyState === 4) {
        document.getElementById("ajax").innerHTML = xhr.responseText;
      }
    };
    xhr.open('GET', 'sidebar.html');
    xhr.send();

So from the code I can assume that the request will only get sidebar.html, which worked properly. But another XML request was shown in the console:

XHR finished loading: GET "chrome-extension://mgijmajocgfcbeboacabfgobmjgjcoja/content.min.css"

Which is obviously from a chrome extension. The questions I thought about (and haven't yet looked up) is about the open() method and whether we can request more than one object that can vary in source (a file or a url link). And if open() support multiple requests, is it better to separate each XML request in a different variable and called with it's own open() method or included in one variable that are called in one method?