This may not actually be a Firefox problem.

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

Secure connection problems have usually been due to antivirus trying to help you with its own certificate but instead making this worse.

https://support.mozilla.org/en-US/kb/troubleshoot-SEC_ERROR_UNKNOWN_ISSUER

The ONLY thing that changed to keep Firefox from working eas the latest Firefox uodate...nice try.

uninstall Firefox. Then Delete the Mozilla Firefox Folders in C:\Program Files and C:\Program Files(x86) Then restart system. Then run Windows Disk Cleanup. 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

Reinstall with Current Release Firefox 57.0 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.

If you come back to Firefox and the problem continues, then:

Check out the first article linked by James. You will notice that the error page has an Advanced button you can click to extract more detailed error information that will help us troubleshoot this problem.

If you see the code SEC_ERROR_UNKNOWN_ISSUER, please refer to the second article that James linked to.

Nope. When trying yo connect to MOZILLA.ORG/privacy/firefox/ AND to MOZILLA.ORG/en-US/firefox/57.0/firstrun/ I get the following warning: "Your connection is not secure." Now I am CERTAIN I am finished with Firefox. Too bad. It was a great browser until they screwed it up!

rototbob88 said

The ONLY thing that changed to keep Firefox from working eas the latest Firefox uodate...nice try.

This has not been a common issue wiith Firefox 57.0 though.

What antivirus client do you have as you can check the settings mention in article.

Hi rototbob88, if you change your mind about Firefox:

CLICK THE ADVANCED BUTTON and copy/paste the detailed information there into a reply.

That will enable us to assist you better.

Also, secure connection errors have affected many users during the past several years, it has nothing to do with changes in Firefox 57.

Sorry, but I'm done. Firefox is naught but a fond memory. Too bad

rototbob88 said

Sorry, but I'm done. Firefox is naught but a fond memory. Too bad

So instead of saying what security software you have including antivirus clients you are just going to give up?

Look after a new major Firefox version update or install on Windows sometimes a antivirus client ends up being a nuisance for them and a setting in it needs changing.

Yup, I'm just going to "give up." If a product requires me to run an obstacle course, run a marathon, then jump through the burning hoops, it's not ready for the market I populate!

Yup, I'm just going to "give up." If a product requires me to run an obstacle course, run a marathon, then jump through the burning hoops, it's not ready for the market I populate!

We actually were suggesting clicking a button to see what's there. Then depending on what you see, we would suggest clicking a link, then a button to copy diagnostic data to the clipboard, then pasting into a reply. Then we would give you the diagnosis.

But never mind.

Since you are not willing to do much, one simple reason for getting secure connection issues is due to the date on OS being wrong perhaps because of battery on motherboard or some other reason.

The other cause and this one has nothing to do with a Firefox version.