I found that after Firefox v29, a LOT of my settings and
add-ons were changed / reset. Try this; Start Firefox in Safe Mode
While you are in safe mode;
Firefox Options > Advanced > General.
Look for and turn off Use Hardware Acceleration.
Then check ALL of your settings. Browser and add-ons. Then restart.

If images are missing then check that you do not block images from some domains.

• Tap the Alt key or press F10 to show the Menu bar.

Check the permissions for the domain in the currently selected tab in "Tools > Page Info > Permissions"

Check "Tools > Page Info > Media" for blocked images

• Select the first image link and use the cursor Down key to scroll through the list.
• If an image in the list is grayed and "Block Images from..." has a checkmark then remove this checkmark to unblock images from this domain.

Make sure that you do not block (third-party) images, the permissions.default.image pref on the about:config page should be 1.

Make sure that you haven't enabled a High Contrast theme in the Windows/Mac Accessibility settings.

Make sure that you allow pages to choose their own colors.

• Tools > Options > Content : Fonts & Colors > Colors : [X] "Allow pages to choose their own colors, instead of my selections above"

Note that these settings affect background images.

See also:

• http://kb.mozillazine.org/Website_colors_are_wrong

There are extensions like Adblock Plus (Firefox/Tools > Add-ons > Extensions) and security software (firewall, anti-virus) that can block images and other content.

See also:

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes
• http://kb.mozillazine.org/Images_or_animations_do_not_load
• http://kb.mozillazine.org/Websites_look_wrong