i havent used the chat system yet (timid) but it looks like it uses java, did you make sure your java is updated to the latest version? Verify Java Version

if that doesnt work, which hopefully it should, then does it give you an error # or code that tells you what happened when trying to load?
also if you have 64bit system you could try using Waterfox, its firefox alternative for 64bit systems ( i use it with windows 7 just fine )

ps; under firefox tools, options, and content, there is a javascript checkbox - might check to see if its checked