HI, please try : 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 59.0.2 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.

Separate Issue; Your System Details shows;

Installed Plug-ins

Shockwave Flash 21.0 r0 Shockwave Flash 29.0 r0
Having more than one version of a program may cause issues. You must remove the older programs. Then get the current full installer.

Flash: Grab the uninstaller from here:

http://helpx.adobe.com/flash-player/kb/uninstall-flash-player-windows.html Uninstall Flash Player | Windows

http://helpx.adobe.com/flash-player/kb/uninstall-flash-player-mac-os.html Uninstall Flash Player | Mac

Then reinstall the latest version.

Note: Windows users should download the active_x for Internet Explorer. and the plugin for Plugin-based browsers (like Firefox).

Note: Windows 8 and Windows 10 have built-in flash players and Adobe will cause a conflict. Install the plugin only. Not the active_x.

Flash Player Version 29.0.0.113

https://get.adobe.com/flashplayer/ Direct link scans current system and browser Note: Other software is offered in the download. <Windows Only>

https://get.adobe.com/flashplayer/otherversions/ Step 1: Select Operating System Step 2: Select A Version (Firefox, Win IE . . . .) Note: Other software is offered in the download. <Windows Only>

See if there are updates for your graphics drivers https://support.mozilla.org/en-US/kb/upgrade-graphics-drivers-use-hardware-acceleration

There is security software like Avast, Kaspersky, BitDefender and ESET that intercept secure connections and send their own certificate.

https://support.mozilla.org/en-US/kb/firefox-cant-load-websites-other-browsers-can

https://support.mozilla.org/en-US/kb/firefox-and-other-browsers-cant-load-websites

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

https://support.mozilla.org/en-US/kb/connection-untrusted-error-message

http://kb.mozillazine.org/Error_loading_websites

• uses an invalid security certificate SSL_ERROR_BAD_CERT_DOMAIN
• configured their website improperly

How to troubleshoot the error code "SEC_ERROR_UNKNOWN_ISSUER" on secure websites https://support.mozilla.org/en-US/kb/troubleshoot-SEC_ERROR_UNKNOWN_ISSUER

Thanks for all the help and links. This is going to be a slow process as I am not very computer literate. My laptop is a Toshiba with Windows 10. I see the Shockwave Flash conflict but neither seems to be active as I have to ask to activate, and a disable or uninstall option is not shown. Any idea how this Insecure Connection comes about? This laptop is just 9 years old, was originally Windows 7 but force upgraded to Windows 10. For most of those years I never had a connection problem. Recently, as part of a new contract, I was given a new modem. Could that have any bearing on the current issue?

OneTrueFriend said

Any idea how this Insecure Connection comes about?

There is no telling until the issue is solved. It might be your security programs, it might be the modem, it might be . . . .

OK Thanks. I will check with ISP about the new modem, too.

Hi OneTrueFriend, we should try to get a little more clarity on the issue.

When you are on the error page, usually you will see an "Advanced" button. Please click the button to get more technical details about the problem and paste them into a reply. In particular, there's usually an ERROR_CODE that helps with the diagnosis.

It is not happening today for some reason. I restored recent extensions which I had disabled, just in case, and it is still not happening, and I can't get it to happen. The error message had mentioned something about another root certificate being needed and about the mozilla.org certificate being invalid. Sorry that I can't help further at this time. It is a total mystery to me. Any tab that was showing the error message previously is now showing the correct page, so I am unable to copy the message.

Hopefully it will stay fixed. Sometimes if the issue is your security software, when you restart the system, the software updates Firefox to be compatible.

If the problem returns, let us know that error code.

I will. Many thanks to you and to all who took the time and trouble to contribute.