Firefox not loading thumbnails on some websites

Question

On many websites, like imageboards, or even sites with icons and other small images, Firefox doesn't load these images.
All I see is a blank box, and in the top left corner it shows an image icon (this would be a ripped image icon if the image could not be found).
The links all work fine, and the full-size image always loads fine, but this is very annoying as its defeating the whole purpose of these galleries.
Often the website loads fine, but as I go further into more pages, the images stop loading; sometimes ones that have been previously loaded too.
I've tried clearing caches, DNS caches, etc. no luck. None of these websites are blocking images (right click -> block images from site), and I have no adblocking plugins or software.
Sites like:
Deviant Art
Imageboards
Facebook (galleries)

Answer 1

Did you check the images properties?<br />
It is possible that the images are from another domain.
*A way to see which images are blocked is to click the favicon (<i>Site Identification</i> icon) on the left side of the location bar.
*A click on the "More Information" button will open the Security tab of the "Page Info" window (also accessible via "Tools > Page Info").
*Open the <i>Media</i> tab of the "Page Info" window.
*Select the first image and scroll down though the list with the Down arrow key.
*If an image in the list is grayed and there is a check-mark in the box "<i>Block Images from...</i>" then remove that mark to unblock the images from that domain.
Also make sure that you allow background images:<br />
Firefox > Preferences > Content : Fonts & Colors: Colors > [X] "Allow pages to choose their own colors, instead of my selections above"
See also:
* http://kb.mozillazine.org/Websites_look_wrong
* http://kb.mozillazine.org/Website_colors_are_wrong