Google 'Connection Untrusted' on Firefox after Windows 10 Upgrade

[Mechta]

I don't know if this due to upgrading to Windows 10, a Firefox upgrade or a Kapersky upgrade, but when I try and use Google it says the connection is untrusted.

This Connection is Untrusted

You have asked Firefox to connect securely to Google, 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.

The only option offered is 'Get me out of here'. Clicking technical details reveals

Google uses an invalid security certificate. The certificate is not trusted because the issuer certificate is unknown. The server might not be sending the appropriate intermediate certificates. An additional root certificate may need to be imported. (Error code: sec_error_unknown_issuer)

How do I resume the normal service I had yesterday?

[Mechta]

It looks as though I have answered my own question by removing Google from my list of search engine, then adding Google Encrypted. This seems to work. I don't know if any functionality has been lost.

[Heathrow Harry]

EVERY time we upgrade Firefox there is a problem -

now we leave it for a few weeks after the announcement of the new version until they get it right

[vulcanised]

I don't think the outdated certificate is particularly significant.

My Bank site carried such an alert for several weeks.