The upcoming Firefox 70, set for release sometime in the Fall of 2019, will warn you if your passwords were pirated.
The Mozilla team is integrating its independent Firefox Monitor service natively into Firefox. The service lists every time e-mail addresses have turned up data breaches, can also directly ping users if an e-mail address is found in such a cull. The idea is to also provide warnings when a site or service being visited using the browser has recently been the target of a breach.
The Firefox Monitor service service will be integrated into Firefox 70 (the current version is number 68), and is actually an implementation of the Have I Been Pwned database, which has been collecting passwords that have been made public without internet users' knowledge through known data leaks.