This script will force Firefox to show broken image icon when image failed loading, wether the image has alt attribute. You can press Alt+R to reload the broken images.
Image without alt. you should see the icon by default. <img src="https://i.am.broken"> Image with blank alt. By the default, you will see nothing. <img alt="" src="https://i.am.broken"> Image with alt attribute. You should see the text in alt attribute. <img alt="There used to be a image, but now it is broken" src="https://i.am.broken">
After installing the script:
If you just want to reload broken images, you can use the following code as the bookmarklet:
3.0.0 (Feb 17, 2021)
2.2.1 (Apr 4, 2016)