From MozillaZine Knowledge Base
Until recently, this preference determined whether or not images loaded in the browser. Specifically, it allowed the user to allow all images, allow all images except third-party images, or block images entirely.
Possible values and their effects
Allow all images to load, regardless of origin. (Default)
Prevent third-party images from loading.
Block all images from loading.
Mozilla Firefox 1.0.x
The checkboxes labeled “Load Images” and “for the originating web site only”, located under “Tools → Options → Web Features”, set this preference to 0 and 1, respectively.
Mozilla Suite and SeaMonkey
The radio buttons labeled “Do not load any images”, “Accept images that come from the originating server only”, and “Accept all images”, located under “Edit → Preferences → Privacy & Security → Images → Image Acceptance Policy”, set this preference to 2, 1, and 0, respectively.
First checked in
Has an effect in