Overview
For security reasons, newer versions of Firefox will block pages with "active" mixed content on HTTPS pages. Unfortunately, this breaks some websites such as the eShop website. But, for sites broken by the Mixed Content Blocker, one can disable the blocker.
Disabling the Blocker
When visiting an HTTPS page with Active Mixed Content, the Firefox location bar looks as follows (note the shield at the left of the locaiton bar -- this shield indicates that mixed content has been blocked):
Clicking on the shield, on will see options to "Learn More", "Keep Blocking", or "Disable Protection on This Page":
If one decides to "Disable Protection on This Page", all mixed content will load, and the page should behave as before.
The shield will disappear. And the Lock icon indicating this is an HTTPS page will be replaced with a Yellow Warning Triangle: