• Check the permissions for the domain in the current tab in "Tools > Page Info > Permissions"
• Check that images are enabled: Tools > Options > Content: [X] Load images automatically
• Check the exceptions in "Tools > Options > Content: Load Images > Exceptions"
• Check the "Tools > Page Info > Media" tab for blocked images (scroll through all the images with the cursor Down key).

If an image in the list is grayed and there is a check-mark in the box "Block Images from..." then remove that mark to unblock the images from that domain.

There are also extensions (Tools > Add-ons > Extensions) and security software (firewall, anti-virus) that can block images.

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the extensions is causing the problem (switch to the DEFAULT theme: Firefox (Tools) > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.com/kb/Safe+Mode

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Thanks the plug-in imglikeopera 0.6.21 has found a problem why that blocked images big thanks