"Your connection is not secure"

[Qqmike]

First time for everything. In 14.04, using Firefox for Ubuntu, 47.0, I just got this:

Your connection is not secure

The owner of www.kubuntuforums.net has configured their website improperly. To protect your information from being stolen, Firefox has not connected to this website.

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.

https://support.mozilla.org/en-US/kb...ot-secure-mean

What does "Your connection is not secure" mean?
When Firefox connects to a secure website (the URL begins with "https://"), it must verify that the certificate presented by the website is valid and that the encryption is strong enough to adequately protect your privacy. If the certificate cannot be validated or if the encryption is not strong enough, Firefox will stop the connection to the website and instead show an error page.
On some websites there is an option to report secure connection errors to Mozilla for statistical purposes ...

[Snowhog]

I'll bring this to SteveRiley's attention.

[Snowhog]

His reply:

If it were a site-wide problem, everyone would see this error. My guess is
that QQ is surfing through a VPN or proxy that's spoofing KFN's certificate.
Because QQ previously visited KFN and received a proper certificate, Firefox
is comparing that one to the new one and noticing that they aren't the same.
HTTP Strict Transport Security (HSTS) is supposed to behave like this.

Is there an error code displayed in QQ's browser? Might require clicking an
"Advanced" or "Technical Details" button. Should be something like this,
including the parentheses:

(Error code: description_of_error_here)

[Qqmike]

If it happens again, I will dig deeper. I don't recall seeing any error codes or "Details" button, but maybe it was there somewhere. Btw, I just have DSL from CenturyLink, out of the box, vanilla Ethernet connection to their modem/router -- no special network setup here, IOW. Thanks.

[Snowhog]

IF it happens again, note the complete URL that is being used; could be a clue there.

[acheron]

Can happen if for some reason your system time/date gets messed up, during which time Firefox does not see some website certificates as being validly in force.

Seems a little unlikely here, as this one has 2 years left to run, so you would expect other sites to cause errors if things were that out, but system clock would be the 1st thing I would check if it happens again.