From zdnet.com
The Firefox browser will soon come with a new security feature that will detect and then warn users when a third-party app is performing a Man-in-the-Middle (MitM) attack by hijacking the user’s HTTPS traffic.
The new feature is expected to land in Firefox 66, Firefox’s current beta version, scheduled for an official release in mid-March.
The way this feature works is to show a visual error page when, according to a Mozilla help page, “something on your system or network is intercepting your connection and injecting certificates in a way that is not trusted by Firefox.”