Perform the suggestions mentioned in the following articles:

• Clear Cookies & Cache
• Clear the Network Cache
• Make sure you are using the "Remember History" setting as described in this article -> Settings for privacy, browsing history and do-not-track

• Start Firefox in -> Diagnose Firefox issues using Troubleshoot Mode to check if your add-ons/extension are causing the problem.
• Also see this article -> Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

Check and tell if its working while using Firefox in Diagnose Firefox issues using Troubleshoot Mode.

If images are missing then check that you aren't blocking images from some domains (e,g, sphotos.ak.fbcdn.net).

• Check the permissions for the domain in the current tab in "Tools > Page Info > Permissions"

• Check that images are enabled: Tools > Options > Content: [X] Load images automatically
• Check the exceptions in "Tools > Options > Content: Load Images > Exceptions"

• Check the "Tools > Page Info > Media" tab for blocked images (scroll through all the images with the cursor Down key).

If an image in the list is grayed and there is a check-mark in the box "Block Images from..." then remove that mark to unblock the images from that domain.

Make sure that you do not block third-party images, the permissions.default.images pref should be 1.

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

There are also extensions (Tools > Add-ons > Extensions) and security software (firewall, anti-virus) that can block images.

Make sure that you allow pages to choose their colors and that you haven't enabled High Contrast in the Accessibility settings.

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

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