A While back, Mozilla partnered with Have I Been Pwned to bring breached site alerts to users in Firefox browser, the service available as a website at monitor.firefox.com and integrated into Firefox also. Now the organization wants to alert the users if the saved login data for a domain in browser matches that of breached data.
For the unknown, Mozilla is working on a new Password Manager for Firefox browser known as Firefox Lockwise, which is currently available as an add-on and behind a pref in about:config. The change in question is targetted for built-in Password manager in Firefox version 70.

With the new change, about:logins will indicate if the saved login was part of a data breach. The login entry provides this message to the user:
“Passwords were leaked or stolen from this website since you last updated your login details” and alerts the user to change the password to protect his/her account. The learn more link takes the user to Firefox Monitor website in a new tab with breach details of the affected site.
Note: The Firefox Lockwise can be enabled in Firefox by changing the below about:config preference value to true.
signon.management.page.enabled
Related articles:
Google takes on Firefox Monitor (Breach Alerts service) with Chrome Password Checkup Extension
Mozilla launches Firefox Monitor Notifications for Firefox users