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localhost cert




I've come across an issue that has forced me to (hopefully temporarily) uninstall the software which I was using to do some SNMP monitoring.

Using Thunderbird for email, Oauth2 (which effectively loads a browser window to authenticate) gets to the page where you click "allow" or "deny" and then goes to a "secure connection failed" page.

After a TB update I was able to determine the issue was that after clicking allow, the browser was attempting to load: (eg) https://localhost/?code=p6pqn9prup79mjffc2nbbg4wgmpdafet

(Edited some characters in the code in case they are identifying)

If I got to the url in normal firefox, I get

localhost uses an invalid security certificate.

The certificate is not trusted because it is self-signed.


The cert details point at the PRTG self signed cert

Has anyone any idea on how to resolve this, other than getting my own "proper" cert?

certificate mozilla thunderbird

Created on Aug 15, 2022 10:07:08 PM

1 Reply




Thank you for your message.

When installing PRTG on a machine, the core server (service which hosts the web server) will automatically use the localhost and network IP addresses of the machine to make PRTG accessible. When enabling HTTPs, the web server will also use a self-signed certificate which is the reason why you get the error MOZILLA_PKIX_ERROR_SELF_SIGNED_CERT.

Therefore, to avoid such issue we recommend to install PRTG on a dedicated machine (physical or virtual) with no other applications (ex thunderbird) installed. This way you can also avoid performance issues.

If you have questions, do not hesitate.


Created on Aug 18, 2022 8:23:59 AM by  Florian Lesage [Paessler Support]

Disclaimer: The information in the Paessler Knowledge Base comes without warranty of any kind. Use at your own risk. Before applying any instructions please exercise proper system administrator housekeeping. You must make sure that a proper backup of all your data is available.