This could be an issue caused by AdAware or Web Companion from Lavasoft.

You can look for a file named dsengine.js in these locations. You should only find channel-prefs.js in the "defaults\pref" location, any other file found here is suspicious.

C:\Program Files\Mozilla Firefox\defaults\pref\
C:\Program Files (x86)\Mozilla Firefox\defaults\pref\

You can look for a file named dsengine.cfg in the main Firefox program folder.

C:\Program Files\Mozilla Firefox\
C:\Program Files (x86)\Mozilla Firefox\

Delete the dsengine.js and dsengine.cfg files when present.

cor-el:

Thanks for the reply.

channel-prefs.js is the only file in the folder c:\program files\Mozilla Firefox\ defaults\pref\.

dsengine.js and dsengine.cfg do not exist in either of these suggested locations either...

Where is the screen shot of the error?

WestEnd: I have attached the screen shot of the error here for your review. Please let me know what you think. In case the screen shot is not viewable, here is the copied text: Your connection is not secure

The owner of www.google.com has configured their website improperly. To protect your information from being stolen, Firefox has not connected to this website.

This site uses HTTP Strict Transport Security (HSTS) to specify that Firefox may only connect to it securely. As a result, it is not possible to add an exception for this certificate.

Learn more…

Report errors like this to help Mozilla identify and block malicious sites

www.google.com uses an invalid security certificate.

The certificate is not trusted because the issuer certificate is unknown. The server might not be sending the appropriate intermediate certificates. An additional root certificate may need to be imported.

Error code: SEC_ERROR_UNKNOWN_ISSUER

Thanks

If the certificate is not trusted (SEC_ERROR_UNKNOWN_ISSUER) then click the blue error message to expand this section and show the certificate chain. You can click "Copy text to clipboard" and paste the base64 encoded certificate chain text in a reply. That will allow us to details like the issuer of the certificate.

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

• always be cautious when you get an 'Untrusted' error message
• never create a permanent exception without investigating the cause and only use this to inspect the certificate

cor-el:

Here is the certificate chain:

https://www.google.com/

Peer’s Certificate issuer is not recognized.

HTTP Strict Transport Security: false HTTP Public Key Pinning: true

Certificate chain:

Since you use MSE which version of Windows O/S are you using right now? I have google.com set as my home pages in IE11, Edge, Chrome and FF but have no problem using the search when it is set as my homepage. I am on W10 with Defender and FF58.

Can you post the certificate chain?

WestEnd,

I am running Windows 7 Professional. I have FF version 58.0.1(32 Bit). I have always had Google set as my homepage in any browser I have used. Now I can't get to Yahoo and Bing is asking me to add the exception when using FF.

I didn't have this issue until I clicked the button that says "my FireFox needed to be sped up", or something like that. Then it created a file on my desktop called "Old Firefox Data".....

cor-el,

This is all that comes up when I click the "Error code: SEC_ERROR_UNKNOWN_ISSUER":

https://www.google.com/

Peer’s Certificate issuer is not recognized.

HTTP Strict Transport Security: false HTTP Public Key Pinning: true

Certificate chain:

csuenram said

cor-el, This is all that comes up when I click the "Error code: SEC_ERROR_UNKNOWN_ISSUER":

Yes, this doesn't seem to be working for users lately.

I you go to a site that isn't so high security, you can use the "Add Exception" button to view the certificate. For example:

https://www.userchrome.org/

Click the Advanced button again, then click the "Add Exception" button (see first screenshot below). We're not really going to add an exception, but we can get a better view of the certificate here.

In the Add Exception dialog, click the "View" button to pop up a certificate viewer. The interesting part is the "Issued by" section. I've marked that on the second screenshot for reference.

On my site, the "Issued by" section shows me "Let's Encrypt Authority X3". What do you see there?

Maybe check SiteSecurityServiceState.txt and remove entries that refer to websites that you want to check.

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

Thank you for your help. Not sure which one actually made it work again as I retried and restarted many times to ensure I followed the steps correctly. I really appreciate your help! It is working now.