Sometimes a problem with Firefox may be a result of malware installed on your computer, that you may not be aware of.

You can try these free programs to scan for malware, which work with your existing antivirus software:

• Microsoft Safety Scanner
• MalwareBytes' Anti-Malware
• Anti-Rootkit Utility - TDSSKiller
• AdwCleaner (for more info, see this alternate AdwCleaner download page)
• Hitman Pro
• ESET Online Scanner

Microsoft Security Essentials is a good permanent antivirus for Windows 7/Vista/XP if you don't already have one.

Further information can be found in the Troubleshoot Firefox issues caused by malware article.

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Check the date and time in the clock on your computer: (double) click the clock icon on the Windows Taskbar.

Check out why the site is untrusted and click "Technical Details to expand this section.
If the certificate is not trusted because no issuer chain was provided (sec_error_unknown_issuer) then see if you can install this intermediate certificate from another source.

You can retrieve the certificate and check details like who issued certificates and expiration dates of certificates.

• Click the link at the bottom of the error page: "I Understand the Risks"

Let Firefox retrieve the certificate: "Add Exception" -> "Get Certificate".

• Click the "View..." button and inspect the certificate and check who is the issuer of the certificate.

You can see more Details like intermediate certificates that are used in the Details pane.

If "I Understand the Risks" is missing then this page may be opened in an (i)frame and in that case try the right-click context menu and use "This Frame: Open Frame in New Tab".

• Note that some firewalls monitor (secure) connections and that programs like Sendori or FiddlerRoot can intercept connections and send their own certificate instead of the website's certificate.
• Note that it is not recommended to add a permanent exception in cases like this, so only use it to inspect the certificate.

Sourjobraato Banerjee - I ran all the programs suggested. Nothing really came up except tracking cookies and YTD browser ext. that isn't used, but must have been installed. Only the last 2 programs picked up these things.

Today I had this happen again while visiting a facebook page that must've had a video or something to it. I got the untrusted connection but didn't give me the second option of "I understand the risks" so I just reset it again. I like to use the Adblocker Plus also on FF & IE. The last time I reset FF (when I started this thread), has been good since till today with the incident listed.

cor-el - time and date is correct. I will pay attention to what comes up with why it is not allowing now that I needed to reset FF over today.

It just seems like a weird bug. I have a laptop that came with windows 8.1 on it and I use FF and I never have any issues on that, but this desktop after I upgraded to 8.1 is getting annoying when using FF. When I had windows 8, FF worked fine LOL.