Web browsers have trouble with mixed content (secure and not secure, https and http) on the same page. With Firefox and Chrome, you may have to approve each page.

Non-https image:

Non-https embedded page (border added for emphasis, usually there won't be one):

If you see this at the top of the content area, but no content below it, the easiest thing to try to see the content is to open it in a new window by clicking on the icon next to the title.

Other ways to show content:

Firefox

You may need to enable each page each time you visit it.

If this is the case, you will see a small grey shield to the left of the URL:

arrow pointing to warning icon Image of mixed content shield.

Click in that shield and in the dropdown, choose "Connection Not Secure," then "Disable Protection for Now"

Chrome

When a page has mixed content, Chrome has a shield at the right of the address bar.

Click the shield and then 'Load unsafe script.'