The new Firefox Monitor service will use anonymized range query API endpoints from Have I Been Pwned (HIBP) This new Firefox feature allows users to check for compromised online accounts while preserving their privacy. Mozilla is working with Troy Hunt creator and maintainer of HIBP to use new hash range query endpoints for breached account data in the Firefox Monitor project. The API adds k-Anonymity to the data that Mozilla exchanges with HIBp to protect individuals who are the subjects of the data from re-identification.”]
Source: https://blog.mozilla.org/security/2018/06/25/scanning-breached-accounts-k-anonymity/