Chrome extension: webRequest.onBeforeSendHeaders behaves strange

Question

I am trying to add a \"Referer\"-HTTP-Header to certain AJAX requests in my Chrome extension. You can\'t change it directly in the AJAX request so I tried to change it using

Answer 1

chrome.webRequest.onBeforeSendHeaders.addListener(function(details) {
     console.log(details);
},{urls: [""]});