Can anyone answer my question?

Check that you do not run Firefox as Administrator.

Right-click the Firefox desktop shortcut and choose "Properties".

Make sure that all items are deselected in the "Compatibility" tab of the Properties window.

• Privilege Level: "Run this program as Administrator" should not be selected
• "Run this program in compatibility mode for:" should not be selected

Also check the Properties of the firefox.exe program in the Firefox program directory.

Thank you very much for your help! Unfortunately, when I uncheck "Run As Administrator" I cannot open Firefox at all.

That is still the required setting to avoid that alert.
Running Firefox as Administrator is not recommended, you only need that is case of an update.

A possible cause is security software (firewall) that blocks or restricts Firefox or the plugin-container process without informing you, possibly after detecting changes (update) to the Firefox program.

Remove all rules for Firefox from the permissions list in the firewall and let your firewall ask again for permission to get full unrestricted access to internet for Firefox and the plugin-container process and the updater process.

See:

• https://support.mozilla.com/kb/Server+not+found

I still get the same box with the same question when I open Firefox.

Thanks!

Are you still running Firefox as Administrator ?

As I said earlier, I can't log in unless I am using it as administrator