CONSOLE WARNING: line 18: Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user's experience. For more help, check https://xhr.spec.whatwg.org/.
CONSOLE ERROR: Failed to load http://www1.web-platform.test:8001/xhr/resources/access-control-preflight-denied.py?token=c0e99821-8c70-4442-be93-a39f69f4827a&command=header: Request header field x-test is not allowed by Access-Control-Allow-Headers in preflight response.
