The name explained it
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.
這個Script會強制Firefox顯示圖片載入失敗的圖示，即使圖片有alt屬性。 按Alt+R會重新載入失敗的圖片。
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:
javascript:void(!function()%7Bfor(const%20o%20of%20document.images)o.complete%26%26!o.matches(%22%5Bsrc%5D%3A-moz-broken%22)%7C%7C(o.src%2B%3D%22%23%22)%7D()%3B)
!image.src.