This has nothing to do with avast HTTPS scanning, but more with the firefox browser alerting to the fact that that connection is not trusted.
Google Chrome does not give that warning.
I get the following test results: Secure HTTPS Connectivity
Secure Connection Successful
We were able to connect securely to your HTTPS server. This means that your HTTPS server is listening for and also responding to secure requests.
SHA-2 Certificate
Your certificate is signed using the SHA-2 algorithm.
Name Match Successful
The server address which you provided matches the server name that is on the SSL certificate.
SSL verification issue (Possibly mis-matched URL or bad intermediate cert.). Details:
ERROR: cannot verify forums.spybot.info’s certificate, issued by ‘/C=IL/O=StartCom Ltd./OU=Secure Digital Certificate Signing/CN=StartCom Class 2 Primary Intermediate Server CA’: Unable to locally verify the issuer’s authority.
Trusted No (No signatures could be verified because the chain contains only one certificate and it is not self signed.)
Not vulnerable to POODLE. forums.spybot.info has a verifiable certificate chain signed with SHA-2, that is NICE.
Not vulnerable to r OpenSSL Heartbleed vulnerability…
By the way Comodo Siteinspector also flags the site as suspicious - Transaction Protection
UNTRUSTED BY MICROSOFT
SSL Issuer: StartCom Class 2 Primary Intermediate Server CA
SSL Expires: 2017-04-23 03:06:13 UTC
Again a SSL certification issue and has nothing whatsoever to do with Avast https scanning.
polonus (volunteer website security analyst and website error-hunter)
I have a red Calomel (extension) warning in firefox, no public audit info available, untrusted connection
One report on WOT:
Auf htxp://www.safer-networking.org/de/mirrors/
leitet der 1.Haupt-Mirror zu einer unzuverlässigen Seite: https://www.mywot.com/scorecard/spybot-now.com "jokalliauer