Hey, I had this same problem. The problem is caused by your computer time and date being off from the actual time and date. There is a very simple solution. Check your date and time on your computer. If it is incorrect change it back to the right time. Make sure the month and year are correct too. That should fix it.

Bypassing the warning

You should only bypass the warning if you're confident in both the identity of the website and the integrity of your connection - even if you trust the site, someone could be tampering with your connection. Legitimate public sites will not ask you to add connection rule exceptions - an invalid certificate can be an indication of a web page that will defraud you or steal your identity.

1.   On the warning page, click I Understand the Risks.
2.   Click Add Exception.... The Add Security Exception dialog will appear.
3.   Read the text describing the problems with this site.
4 .  Click Confirm Security Exception if you want to trust the site. 

I hope it was useful