Your connection is not secure

[Roffen]

XP machine, message: "Your connection is not secure... This site uses HTTP Strict Transport Security (HSTS) to specify that Firefox may only connect to it securely. As a result it is not possible to add an exception for this certificate."

What, if anything, can I do?

[Mcinwwl]

1. Which version of Firefox do you use?

2. Which website do you refer to?

3. do you install POSReady 2009 updates or not?

[dencorso]

Looks like problems with antivirus software or a missing certificate. This report does not refer to XP but may be enlightening nonetheless: https://www.bleepingcomputer.com/news/software/mozilla-halts-firefox-65-rollout-due-to-insecure-certificate-errors/

[RED-CHAMBER]

I was plagued with those messages until in my antivirus, in network configuration, specified not to analyze the encrypted connections.

Edited February 6, 2019 by RED-CHAMBER