why can't I connect to paypal.com?

I can't access paypal.com - firefox gives me the following error message: This Connection is Untrusted You have asked Firefox to connect securely to www.paypal.com, but we can't confirm that your connection is secure. Normally, when you try to connect securely, sites will present trusted identification to prove that you are going to the right place. However, this site's identity can't be verified. What Should I Do? If you usually connect to this site without problems, this error could mean that someone is trying to impersonate the site, and you shouldn't continue. This site uses HTTP Strict Transport Security (HSTS) to specify that Firefox only connect to it securely. As a result, it is not possible to add an exception for this certificate. www.paypal.com uses an invalid security certificate. The certificate is not trusted because the issuer certificate is unknown. (Error code: sec_error_unknown_issuer) I like using PayPal - how do I get this to work? I am using a new computer and using Kaspersky Internet Security for the first time.