This can happen if the page is opened in a (i)frame.

You should be able to verify that via the right-click context menu. If there is a This Frame entry then you can try to open the page in a new tab. Looks that the server isn't configured properly and doesn't send a complete certificate chain that ends with a built-in root certificate.

You can inspect the certificate chain via a site like this:

• http://www.networking4all.com/en/support/tools/site+check/

I have the same issue when i try to upgrade to any version of firefox 20+. The option "i understand the risk" is missing since versions 20+.

This is already the case if you try to connect to "bugzilla.mozilla.org". So, with the newer version you couldn't even report that error to the bug database.

(Windows XP, admin managed user profiles - in case of relevance)

Up to version 19 everything runs perfectly. Since version 1. But starting with version 20, its no more possible to define any certificate exception.

Well: I know how to import certificates by hand, but since it is not acceptable to burden normal users with that, and since this is not the only critical issue with firefox 20+, someone should really take it into quality assurance!

The issue remains with every addon and every plugin deactivated. As soon as the browser is back downgraded to version 19, everything returns to be working.

Thus, the issue has nothing to do with any data in the user profile (i use the same user profile between the two browser versions). It is solely based on the program code in the version 20+ program installation folder.

It MAY have anything to do with configuration of user rights in the os environment. Since i have sophisticated user rights minimization in place from the first days of my win xp times on, it is not unusual that from time to time there come up some programs not compatible with minimal user rights policies. I am used to correct such issues while keeping minimal impact on the overall system policies.

A first run with sysinternals procmon didn't show a sufficient hint in this case. I would need additional direction. And maybe it isn't attributed to user rights at all...

Check the date and time in the clock on your computer: (double) click the clock icon on the Windows Taskbar.

• https://support.mozilla.org/kb/Secure+Connection+Failed

You can retrieve the certificate and check details like who issued certificates and expiration dates of certificates.

• Click the link at the bottom of the error page: "I Understand the Risks"
• Let Firefox retrieve the certificate: "Add Exception" -> "Get Certificate"
• Click the "View" button and inspect the certificate and check who is the issuer.

You can see more details like the intermediate certificates that are used in the Details tab.

Note tat Some firewalls monitor secure (https) connections and send their own certificate instead of the website's certificate.

Make sure that you do not run Firefox in (permanent) Private Browsing mode (Never Remember History).

• https://support.mozilla.org/kb/Private+Browsing

• Tools > Options > Privacy > Firefox will: "Use custom settings for history"
• Deselect: [ ] "Always use private browsing mode"