I just had a window come up saying that my Mozilla security needs upgrading, with a download button. I have had this before when visiting this site. Just a friendly warning - if it comes up do not click the download button as it is malware.
There is some sort of intermittent problem, but as long as you don't click on anything it appears to be ok. I just closed Firefox then reopened it, and it seems to be ok now, but you can never be too careful!