Hopefully this support article is what you need: http://support.mozilla.com/en-US/kb/Websites+look+wrong

It is possible that you clicked "Block Images" in the right click context menu while trying to save an image.<br /> Check the image exceptions: Tools > Options > Content: Load Images: Exceptions - See [[Options window - Content panel]]<br /> <br /> 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.<br /> A click on the "More Information" button will open the Security tab of the "Page Info" window (also accessible via "Tools > Page Info").<br /> Open the <i>Media</i> tab of the "Page Info" window.<br /> Select the first image and scroll down though the list with the Down arrow key.<br /> 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.<br /> <br /> See also [[Images or animations do not show]] and http://kb.mozillazine.org/Images_or_animations_do_not_load<br />