Hmm, is this the only site where Firefox gives you a certificate error? Normally you should not have certificate problems with well-run sites. Frequent certificate errors can indicate one of the following:

(1) Error in your system's date, time, or time zone, which throws off certificate validity checks. Sometimes allowing computers to use an internet-based time source can introduce this problem.

(2) Firefox not being set up to work with your security software that intercepts and filters secure connections. Products with this feature include Avast, BitDefender, Bullguard, ESET, and Kaspersky; AVG LinkScanner / SurfShield can cause this error on search sites.

(3) On Windows 10, Firefox not being set up to work with the parental control software Microsoft Family Safety. (To test by turning it off, see: http://windows.microsoft.com/en-us/wi.../turn-off-microsoft-family-settings)

(4) Malware on your system intercepting secure connections.

If you have any of those specific security products mentioned in #2 or #3:

That would be the first thing to check. This support article will walk you through it: How to troubleshoot security error codes on secure websites.

If none of those ring a bell:

We would like to rule out malware as a potential issue. Have you created "exceptions" for any sites?

1- system date and time ok 2 - How would I set up Eset to work with Firefox? 3 - running windows 7 4 - only created exception for getfirebug.com and that was back in May.

Firefox and Firebug were running fine until I updated Firefox. I'm trying to use firebug for selenium but I can't get it installed.

You can import the ESET signing certificate. It's been a while since I checked the ESET user guides, but here's a post from January with links: https://support.mozilla.org/questions/1106975#answer-837219

Or... during your update, did the Refresh feature run? The tell-tale signs are that you will find an Old Firefox Data folder on your desktop, and you will need to reinstall some extensions.

In that case, you could copy the old cert8.db file from the profile folder inside Old Firefox Data to your current one, and that would restore the trust in all certificates added prior to the Refresh. If you are not familiar with the locations of Firefox profile folders, I can provide the full steps for this option.

Thank you so much for your help! I had to change ESET SSL to interactive mode, install Firebug and and FirePath, and the return ESET SSL to automatic mode. It's working now. Thanks again!

Karen