Can not watch video for getting boosters. Happened today

"This Connection is Untrusted

You have asked Firefox to connect securely to app.videostat.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.

app.videostat.com uses an invalid security certificate. The certificate expired on 10/27/2013 10:45 AM. The current time is 10/28/2013 12:07 AM. (Error code: sec_error_expired_certificate)"

Please advice me. Many thanks !!!