You can modify your mixed display (passive) content preferences here:

  1. In a new tab, type or paste about:config and press Enter/Return. Click the button promising to be careful.
  2. In the filter box, type or paste mix and pause while the list is filtered.
  3. These are the relevant preferences:
    1. security.mixed_content.block_display_content is set to false by default, meaning Firefox will load http images in pages loaded on https addresses. When this occurs, the "warning lock" icon will be displayed in the address bar. Option: Double-click to toggle the value to true. A broken image icon should appear for those images instead.
    2. security.mixed_content.upgrade_display_content is set to false by default, meaning that when you block http images in a page loaded on an https address, Firefox won't try to upgrade the image address to https. Option: Double-click to toggle the value to true. If the server hosting the image supports HTTPS connections, the image should appear in the page instead of the broken image icon.

Reload the page after making changes to trigger application of the updated preference value.


This <img> tag uses an HTTPS (secure) address:

This <img> tag uses an HTTP (insecure) address but is upgradable:

This <img> tag uses an HTTP (insecure) address and is not upgradable:

Copyright © 2019 Jefferson Scher. Updated 8/27/2019.