To remove this alert follow these simple rules. After you do something reload. If there’s no more alerts, you succeeded. Otherwise go on making changes until the message disappears.
1. Change all http:// resource links to https://. The doctype is not a problem. All others (images, css, javascripts, iframe pages) should be https://.
2. Change all about:blank links (yep, these are unsecure) to a blank file that exists and is a https:// link.
3. Check if there are any hidden requests to http:// (it won’t show https:// request with the default setting). Change them to https://.
4. Check if any iframes have # for src. Change them to something that is a https:// link and exists. Looks like # is actually an alias to about:blank. Find any resources that return an error.
