hi Waldo63, first please make sure that the date, time & timezone are set correctly on your system. if this doesn't solve the issue (or it is already set properly), a solution depends on the individual circumstances:

• what is the error code shown when you click on advanced on that error page?
• please also give us more information about the error by clicking on the error code, copying the text to the clipboard and then pasting it here into a reply in the forum.

thank you!

Date,time and time zone are set correctly. Here is the error code info you asked for.

https://www.yahoo.com/

Peer’s Certificate issuer is not recognized.

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

Certificate chain:

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The safe browsing setting in my antivirus program which is Bull Guard is there for a reason. One of the solutions on the Firefox help page is this

Bullguard

In Bull guard security products you can disable the interception of secure connections on particular major websites like Google, Yahoo and Facebook:

   Open the dashboard of your Bull Guard application.
   Click on Antivirus settings > Browsing.
   Uncheck the Show safe results option for those websites which are showing an error message. 

Now, the reason I was saying that safe browsing is there is to help keep you safe. Why would you, or should you have to do this in your anti virus program. I'm sorry if this sounds a bit skeptical but Firefox has before tried to say what is safe and what isn't in spite of the fact that your anti virus program isn't giving you a warning. As I said before also in the details section of my question is that this problem did not occur until the new upgrade to 50.0

Also these errors are coming up in youtube, google, and bing.

please try to reinstall your bullguard security product while firefox is closed or else get in contact with their support in order to inquire how you can get it to add its certificate that it's using to intercept secure connections into the firefox trust store again...

Thank you Phillip. I uninstalled Bull Guard and Firefox. I then started over and reinstalled Bull Guard first and then Firefox and now it is working beautifully. Thanks again, Jack