HI, please list your add-ons/Extensions as well as what Security Software you are running please.

Security software like Avast/AVG, Kaspersky, BitDefender, ESET sometimes McAfee can present issues with their scanners.

• https://support.mozilla.org/en-US/kb/secure-connection-failed-error-message#w_avast-and-avg-security-products

also

• https://support.mozilla.org/en-US/kb/secure-connection-failed-error-message

If not running those named please try : SAFE MODE

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

In Firefox Safe mode these changes are effective:

• all extensions are disabled (about:addons)
• default theme is used (no persona)
• userChrome.css and userContent.css are ignored (chrome folder)
• default toolbar layout is used (file: localstore-safe.rdf)
• Javascript JIT compilers are disabled (prefs: javascript.options.*jit)
• hardware acceleration is disabled (Options > Advanced > General)
• plugins are not affected
• preferences are not affected

TEST''''is issue still there ?

Yes, right out of the box!

Let's assume there's a good explanation for the error -- a new installation of Firefox isn't set up to work with any "man in the middle" security suite like AVG, Avast, Bitdefender, ESET, or Kaspersky. What can you do? Either:

• The security software will set up Firefox automatically at your next system startup or by using a button in the software's interface (simplest)
• You can disable the "man in the middle" feature (see: How to troubleshoot security error codes on secure websites -- the new AVG is similar to Avast); this may improve performance by removing one level of filtering
• If necessary, you can manually import a signing certificate into Firefox's certificate store (typically provided with the software)
• You can set Firefox to trust certificates that your OS collects instead of needing to be separately set up

"The owner of support.mozilla.org has configured their website improperly. To protect your information from being stolen, Firefox has not connected to this website."

It is your durned website that your durned browser will not access.

CylancePROTECT is my anti-virus. But it is YOUR browser that is telling me that YOUR website is improperly configured.

And Safe Mode does not change this - still get the error message.

And I have installed no extensions, no plug-ins, no themes, made no changes to the configuration, nothing - this is a cherry install on a Win 10 box - will not access Mozilla.org simply as installed.

Let's do a cherry clean install with a Full Version Installer : uninstall Firefox. Then Delete the Mozilla Firefox Folders in C:\Program Files , C:\Program Files(x86) & C:\ProgramData Then restart system. Then run Windows Disk Cleanup. (Note: This should be Pinned and run Weekly, If never done below expect 10's of gig's) Then run it again and click the button that says Cleanup System Files. Note: your Firefox Profile is saved. But you should make a back up before you do :

• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles
• https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer

Reinstall with Current Release Firefox 61.0.2 with a Full Version Installer

• https://www.mozilla.org/firefox/all/

Please let us know if this solved your issue or if need further assistance.

Hawk3 said

CylancePROTECT is my anti-virus.

Does the product intercept browsing requests? That could cause this issue with all HTTPS addresses.

Since this is your corporate software, you might try the following workaround. It is less protective than some other approaches, but I suspect that would be your IT Department's problem and not yours.

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful or accepting the risk.

(2) In the search box above the list, type or paste root and pause while the list is filtered

(3) Double-click the security.enterprise_roots.enabled preference to switch the value from false to true, so Firefox trusts the contents of the Windows certificate store rather than only its own certificate store

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.

Hawk3 said

"The owner of support.mozilla.org has configured their website improperly. To protect your information from being stolen, Firefox has not connected to this website." It is your durned website that your durned browser will not access. CylancePROTECT is my anti-virus. But it is YOUR browser that is telling me that YOUR website is improperly configured. And Safe Mode does not change this - still get the error message.

No *.mozilla.org site including support.mozilla.org has any secure connection issues.

Firefox 61.0.2 itself from mozilla.org does not have issues with connection to https:// pages otherwise it would be a very hot topic here.

Common reason for secure connection issues with Firefox on Windows can be due to wrong date/time set on OS, a software or hardware Firewall perhaps, a VPN or Proxy being used.

In the past few years the most common cause of this issue you are experiencing have been due to antivirus software (if setting is checked in client like in article) inserting its own certificate it attempt to keep you safe but instead is the cause of the secure connection issues. https://support.mozilla.org/en-US/kb/error-codes-secure-websites#w_antivirus-products

https://support.mozilla.org/en-US/kb/what-does-your-connection-is-not-secure-mean