If you try to upload files to slideshare from Chrome and the upload fails with a status code of 307 Internal Redirect (in Network tab of dev console) with Non-Authoritative-Reason: Delegate as response header and you get XMLHttpRequest cannot load http://uploads-slideshare.s3.amazons.com/. Response for preflight is invalid (redirect) error, means that your browser is redirecting an http request to https and it is failing. In my case it was because of the HTTPS Everywhere chrome extension. You want to uncheck Amazon Web Services from the extension for the upload to work. Also, if you have PrivacyBadger, then adjust it for the site if login fails.