The security tool is the result of a partnership between Mozilla and HaveIBeenPwned.com (HIBP), a site set up by security researcher Troy Hunt that includes a database of email addresses that are known to have been compromised in data breaches.
Thanks to the partnership, Firefox is able to check email addresses against the HIBP database via a method of anonymized data sharing (full details can be found in Troy Hunt's blog post). The new tool builds on Firefox's existing HIBP integration, which tells users if a site they are visiting was previously exposed in a data breach.
In February, password management app 1Password announced its own partnership with HIBP, which lets users check that their passwords haven't been leaked online. Since that time, developers AgileBits have built the Pwned Passwords database list into its 1Password desktop apps. As of today, users can also search HIBP from directly within 1Password via the Watchtower feature in the web version of the product.
Mozilla says it will begin trialling the new integration between HIBP and Firefox to make breach data searchable over the coming weeks.
Firefox Quantum is available for macOS as a free download directly from the Mozilla website.