Starting in Firefox 70, Mozilla aims to have the browser report when any of your saved logins were found in data breaches. This will be done through their partnership with the Have I Been Pwned data breach site.

Mozilla is slowly integrating their independent Firefox Monitor service and the new Firefox Lockwisepassword manager directly into Firefox.  Mozilla is also considering premium services based around these features in the future.

As part of this integration, Firefox will scan the saved login names and passwords and see if they were exposed in a data breach listed on Have I been Pwned. If one is found, Firefox will alert the user and prompt them to change their password.

Källa: Firefox to Warn When Saved Logins are Found in Data Breaches