The appearance of sites, like Gmail, look weird, like incomplete ...

I use Win XP and Firefox 3.6.12. At first I thought it was my Gmail, but then I noticed that other sites do not have the proper appearance. ...

I use Win XP and Firefox 3.6.12. At first I thought it was my Gmail, but then I noticed that other sites do not have the proper appearance. It's like the pages are incomplete. Not all features that are normally there appear. The funny thing is that this happens on my work computer as well. If I use another browser such as Chrome, all is ok, just Firefox is not working properly. I though it might be a setting in about:config but I have no idea where to go in those settings and what to change.