Does the same thing happen in Safe mode?

Can you attach a screenshot that shows the error message? *https://support.mozilla.org/en-US/kb/how-do-i-create-screenshot-my-problem *use a compressed image type like PNG or JPG to save the screenshot Firefox 51+ will mark HTTP connections with a padlock with a strike through and shows "Connection is Not Secure" if you click the Control Center 'i' button at the left end of the location/address bar. You can disable the warning that opens when you type in a name/password field by setting this pref to false. *security.insecure_field_warning.contextual.enabled = false You can remove the warning in the location bar by setting this pref to false on the <b>about:config</b> page. *security.insecure_password.ui.enabled = false See also: *https://support.mozilla.org/en-US/kb/insecure-password-warning-firefox *https://support.mozilla.org/en-US/kb/how-do-i-tell-if-my-connection-is-secure *https://support.mozilla.org/en-US/kb/what-does-your-connection-is-not-secure-mean