Is this from work or from home? And what kinda firewall and A/V are you using? Those are the likely suspect here.

WestEnd said

Is this from work or from home? And what kinda firewall and A/V are you using? Those are the likely suspect here.

This is happening both at work and at home. Standard Windows 10 firewall and Defender for the AV.

What would cause the firewall or the AV to only affect Firefox?

A/V Defender is also a filter check it's filter and see what is says.

WestEnd said

A/V Defender is also a filter check it's filter and see what is says.

Not finding any filter info within Defender.

Hi, sometimes something that you find irrelevant to the question is the answer. Seems not this time. But fyi : There is security software like Avast/AVG, Kaspersky, BitDefender and ESET that intercept secure connections and send their own certificate.

One issue that seems more common lately is Firefox's Tracking Protection feature. When it is blocking content in a page, a shield icon will appear at the left end of the address bar next to the padlock icon. This article has more info on managing this feature: Tracking Protection https://support.mozilla.org/en-US/kb/tracking-protection

If not the above and since no information came about your Extensions and non supplied please : Try Firefox Safe Mode to see if the problem goes away. Firefox Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes).

If Firefox is open, you can restart in Firefox Safe Mode from the Help menu:

• Click the menu button , click Help and select Restart with Add-ons Disabled.

If Firefox is not running, you can start Firefox in Safe Mode as follows:

• On Windows: Hold the Shift key when you open the Firefox desktop or Start menu shortcut.
• On Mac: Hold the option key while starting Firefox.
• On Linux: Quit Firefox, go to your Terminal and run firefox -safe-mode
  (you may need to specify the Firefox installation path e.g. /usr/lib/firefox)

When the Firefox Safe Mode window appears, select "Start in Safe Mode".

If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, theme, or hardware acceleration. Please follow the steps in the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article to find the cause.

To exit Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.

When you figure out what's causing your issues, please let us know. It might help others with the same problem.

If the above does not help, could you give more details on how Firefox is communicating to you that the site is blocked, or what symptoms you're encountering. For example:

• You get a red warning page. See: How does built-in Phishing and Malware Protection work?

• You get "Your connection is not secure". See: What do the security warning codes mean?

• You get "Secure Connection Failed". See: Secure connection failed and Firefox did not connect.

• You get a different error page instead of the expected page.

• You get a blank page.

• Something else.

The problem has gone away. Today I can nav to any site without issue.

I did a little more checking yesterday and I ended up on a page saying that the site was blocked by OpenDNS content filtering with a with a message about not allowing sites that promote sin.

I don't use any of OpenDNS services so not sure how that got in the mix of blocking things.

OpenDNS can be used as a content filter, perhaps someone either on your computer, or the person who manages your network set it up?

Either way, not a Firefox problem.

Tyler Downer said

OpenDNS can be used as a content filter, perhaps someone either on your computer, or the person who manages your network set it up? Either way, not a Firefox problem.

I do not share any of my computers and I manage the networks.

The issue affected only Firefox on two different computers and two different networks. On both, Edge and Chrome had no issues.

The problem went away on it's own so I guess I'll never know for sure if it was a Firefox problem or not.

If you had an openDNS error message, than it isn't a Firefox issue.

Tyler Downer said

If you had an openDNS error message, than it isn't a Firefox issue.

The OpenDNS was not the initial issue or message. That didn't show up til later in the game. The original symptom was a Firefox error message.

Either way, the problem resolved itself without your input.

Thanks to those who offered assistance.