Note: Some versions of Quantum change how the data files are set up, so they are not backward compatible.

Have you tried Firefox and/or the computer in Safe Mode?

Not sure about your reference to Quantum, but safe mode doesn't help. Is there any way to get into the proxy settings? That's most likely the problem, since there isn't a proxy setup here.

You can check the date and time and time zone in the clock on your computer: (double) click the clock icon on the Windows Taskbar.

• https://support.mozilla.org/en-US/kb/what-does-your-connection-is-not-secure-mean
• https://support.mozilla.org/en-US/kb/troubleshoot-time-errors-secure-websites
• https://support.mozilla.org/en-US/kb/secure-connection-failed-error-message

You can check if there is more detail available about the issuer of the certificate.

• click the "Advanced" button show more detail
• click the blue error text (SEC_ERROR_UNKNOWN_ISSUER) to show the certificate chain
• click "Copy text to clipboard" and paste the base64 certificate chain text in a reply

If clicking the blue error text doesn't provide the certificate chain then try these steps to inspect the certificate.

• open the Servers tab in the Certificate Manager
  • Options/Preferences -> Privacy & Security
    Certificates: View Certificates -> Servers: "Add Exception"
• paste the URL of the website (https://xxx.xxx) in it's Location field

Let Firefox retrieve the certificate -> "Get Certificate"

• click the "View" button and inspect the certificate

You can see detail like the issuer of the certificate and intermediate certificates in the Details tab.

Since the websites Firefox claims it can't verify include google.com, yahoo.com and mozilla.org, I presume the problem isn't related to certificates at all, but to the browser's incorrect settings - which can't be changed even when I run it as the administrator. What is the hack to get into the network settings?

fgranlund said

Not sure about your reference to Quantum

Quantum is the name of the current versions of Firefox.

Is there any way to get into the proxy settings?

Type about:preferences#advanced<Enter> in the address bar.

Under Advanced, Select Network.

[56+] Type about:preferences#general<enter> in the address bar. Look for Network. +++++++++++++++++++++ Look for Configure How Firefox Connects and press the Settings button. If you are using a proxy, make sure those settings are correct. If there is no proxy, first try No Proxy. If there is a problem, then try System Proxy.

Some problems occur when your Internet security program was set to trust the previous version of Firefox, but no longer recognizes your updated version as trusted. Now how to fix the problem: To allow Firefox to connect to the Internet again;

• Make sure your Internet security software is up-to-date (i.e. you are running the latest version).
• Remove Firefox from your program's list of trusted or recognized programs. For detailed instructions, see

Configure firewalls so that Firefox can access the Internet {web link}

cor-el said

You can check the date and time and time zone in the clock on your computer

fgranlund said

Since the websites Firefox claims it can't verify . . . . .

Certificates are time/date sensitive. If the computer's clock setting are wrong, you will have problems.

I can get in to the network settings tab, but all the choices are greyed out and unavailable - including the correct one (no proxy). Is there a setting somewhere else to correct that?

If the connection settings are disabled then it is possible that your computer is set up by your IT department to use the company's proxy.

In that case you can set this pref to true on the about:config page in case other software adds its root certificate to the Windows certificate store.

• security.enterprise_roots.enabled = true

You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.

• http://kb.mozillazine.org/about:config

. . . Except that it's a home computer and there is no proxy. However, the statement "security.enterprise_roots.enabled = true" is in the config settings and is "locked" so it can't be changed. Is that why it claims every website on the net is unverified?

Use these links to create a new profile. Use this new profile as is. Is the problem still there?

https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible

http://kb.mozillazine.org/Profile_folder_-_Firefox#Navigating_to_the_profile_folder

https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

Type about:profiles<enter> in the address bar.

Per the instructins at the first link, I created a new (default) profile by re-naming the profiles.ini file. When I re-started Firefox, it was unable to verify the mozilla.org privacy page it tried to open and gave me the "secure connection failed" error message again. I then checked the network settings box and found the "no proxy" selection still disabled (along with most of the others). I already uninstalled and reinstalled Firefox and tried running it as administrator, but still can't get into the network settings.

Okay, so the problem is in the computer. Did you try the Computer in Safe Mode with Networking?

It is possible that your IT department has locked some settings.

You can check the about:policies#active page in Firefox 63+ to see if there are policies active.