Mixed Content Errors?
<meta HTTP-equiv="Content-Security-Policy" content="upgrade-insecure-requests">
Put this in between the head tags in your header template to get rid of mixed content errors on the entire site. Alternatively, you can put it in the head section of any individual pages that have mixed content errors.
A Word of Caution
This is not magic. It upgrades all HTTP requests to HTTPS before the browser can make them. This means that if there isn’t an HTTPS version of the resource available, the request will fail and you won’t get the resource. Read more here.
If you’re trying to serve your site over HTTPS, this is how it has to be. If you don’t want mixed content errors, you simply cannot load insecure resources. I hope this helps. It certainly helped me get rid of my last few mixed content errors when I switched to HTTPS.