Q:

Why Google Chrome complains about mozilla.org identity?

On a "brand new" (but fully updated) Windows XP installation (an Asus EeePC that I restored to factory setting and than updated with all Microsoft's upgrades) I installed a few days ago Google Chrome.
Today I opened Chrome and browsed https://www.mozilla.org to download Firefox.
I was suprised to see Chrome alerting that, while the ssl certificate was fine, "the identity of the site cannot be verified" and thus the certificate could have been revoked.
I checked it twice, googled a bit looking for issues in the DigiCert certificates and or in the Mozilla's one, found nothing and turned back to my main task.
I downloaded the Firefox installer (Firefox Setup Stub 33.1.1, signed by Mozilla Corporation on 14/11/2014 at 04:36:30AM), and despite the warning, I installed the browser to test a few web pages.
After a few minutes I closed Firefox and Chrome. Than I opened Chrome and browsed to https://www.mozilla.org again, and know what? No warning anymore! 
Out of curiosity I uninstalled Firefox entirelly (suspecting than the installer had installed a new, potentially broken, certificate), but the Chrome warning about the Mozilla certificate was still missing.
Can anybody explain what's happened? Why Chrome changed his own opinion after the Firefox's installation?
Note that I know that windows XP isn't supported anymore by Microsoft, but I can't see how this relates to Chrome's opinion on the Mozilla's certificates!

A:

Check if you're running Chrome 39, there are major changes to the way some certificates are treated - e.g. Chrome 39 starts to penalize sites with long-lived SHA1 certificates
This release warns about SHA1 certificates that expire in 2017. Versions 40 and 41 will increase the scope of the warnings to include certificates that expire in 2016. 
More info can be found here:
http://googleonlinesecurity.blogspot.com/2014/09/gradually-sunsetting-sha-1.html

