How do I fix this? I think I might have picked up a virus or something that has made my computer or browser read valid security certificates as expired:

The certificate is not trusted because the issuer certificate has expired.
The certificate expired on 06/05/2011 00:59.

(Error code: sec_error_expired_issuer_certificate)

The certificates are obviously valid. The one above until 2011.
I’m finding myself have to manually make exceptions for every page I visit.

Can anyone help me?