https://thenextweb.com/security/2018/11/15/firefox-will-notify-you-when-you-visit-breached-websites/

Future versions of Firefox will warn the user when they wander onto a website that’s been the victim of a recently-reported data breach.

The tool, called Firefox Monitor Notifications, is available now in Firefox Quantum and will be rolled out to users of the mainline browser in the coming weeks.