Data breaches are an unfortunate reality of the modern age. Compromised data spreads very quickly in these circles and can cause headaches for affected users. To make sure that you take appropriate actions if you find yourself in such a position, Firefox will start to warn users if their saved logins surface in a data breach.
Mozilla says that Firefox will do this as part of a partnership with the Have I Been Pwned data breach site. Mozilla is linking up its independent Firefox Monitor service and the Lockwise password manager with the Firefox browser directly. This will enable the browser to inform you should your saved logins ever appear in a data breach.
The browser will scan the saved login names and password to check if they have been exposed in a data breach that’s listed on Have I Been Pwned. If it finds a match, Firefox will immediately inform the user and urge them to change their password.