Hi princesspiggy,
This problem only affects Firefox - if you don't use that, then you're fine.
The SSL certificate does two things, it confirms that we are who we say we are and that you can trust us; and it also encrypts the traffic. The problem with Firefox is the confirming who we say we are - it would still be encrypted, although I would recommend against processing an order with any sort of SSL certificate error.
We're working on it, and hope to get it resolved in the next hour or so - we know it isn't anything malicious, just a problem with the setup of the certificates.
Again, non Firefox users will be unaffected. Hope that helps! Remember, we're here to help if you need us (live chat at the bottom).