Web pages content display issues

There has been issues going on my campus network with some webpages not appearing to show the entire content for users on all vlans except for the wireless Guest-Wlan setup on a Cisco 4400 WLAN controller (3 controllers actually). The only thing seen on these specific website homepages are the plain text content but no images or similar. However when the same internal user gets on to the Guest wireless, it shows perfectly fine.(Attachment)
Other setups on the network include:
A Cisco ASA 5500 series firewall
A TrendMicro gateway appliance which does only the content filtering
All connecting to two Core 3560 switches.
In which direction exactly should we take the troubleshooting steps, since it has been really hard to find the source of this problem. Any help is very much appreciated.

I was also facing the same problem with my Google chrome but I followed the following steps:

If you notice squares showing up in the web pages you visit instead of text, try manually overriding the web page's encoding:

• Open your web browser.
• Click the Tools menu on the page menu.
• Select Encoding,Encoding may differ as per your web browser.
• Either choose one of the encodings listed or choose Auto detect. If you turn on the auto detect mode, Google Chrome analysis the content on the web page to recommend the most suitable encoding.

Yeah....I was also facing the similar issue in my Firefox, web pages doesn't open properly, content doesn't display clearly, text overlaps with other text and some parts of the page are hidden.

What is your operating system and which version of Firefox are you using ?

This does not seem to be a browser issue - we have kind of ruled that out since it happens on any windows or mac/ IE/Firefox. The only way the pages would work properly is for the users to get on the Guest-WLan.