This article will explain what mixed content is and what you can do about it.
If a web page loads on HTTPS, yet one of the images, documents, or links to external references are on HTTP this is know as mixed content because some of the content you see is being securely transmitted over HTTPS while some of it is not. As a result, your browser may block the HTTP (insecure) content or show mixed-content warnings. See Google's Security Blog concerning changes to how they handle mixed content.
To ensure that sites do not have mixed-content, site owners should make sure that all links within their site are relative, and that links to external sites refernce HTTPS.
You can Download a Mixed Content Report, Address Items in a Mixed Content Report, and Enable HTTPS by Default to ensure all web content is rendered securely. Please contact our Technical Support Team if you have any questions.