Check the image exceptions: Tools > Options > Content: Load Images: Exceptions - See Options window - Content panel

A way to see if images are blocked is to click the favicon (Site Identification icon) on the left side of the location bar and click the "More Information" button. This will open the Security tab of the Page Info window (also accessible via Tools > Page Info). Go to the Media tab of that Page Info window. Select the first image and scroll down though the list with the Down arrow. If there is a tick-mark in the box Block Images from... then remove that mark to unblock the images from that domain.

See also: Images or animations do not show http://kb.mozillazine.org/Images_or_animations_do_not_load

Also, and although possibly not related to your problem, I have to remind you that the version of Firefox you are using at the moment has been discontinued and is no longer supported. On top of this, it has known unpatched bugs and security problems. I urge you to update to the latest version of Firefox, for maximum security, stability, performance and usability. You can get it for free, as always, at getfirefox.com.