This is probably not the right forum for this but check whether your firefox is at the latest version. Are you on a trusted network? I.e. not some coffeeshop wifi or a hotel wifi?
I use IE and I get the certificate errors on some Adobe sites as well...
This is a private network.
I updated Firefox before I sent the original Message.
It is probably just the way Firefox and Internet Explorer are interpreting the security cert.
In my Mac machines, neither Firefox, Safari or chrome throw up messages like that. You should see what signing authority the certificate that the website wants to use is set to.
Sent from my iPhone