Firefox Quantum Monitor Will Show You Breached Site Notifications

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Firefox Quantum is to provide users with an indication of a site breach notification with an alert appearing as an alert when a site is visited.

While using the Firefox Quantum browser, when you land on a site that’s been breached, you’ll get a notification. You can click on the alert to visit Firefox Monitor and scan your email to see whether or not you were involved in that data breach. This alert will appear at most once per site and only for data breaches reported in the previous twelve months.

[blog.mozilla.org...]

Webmasters can find out more by following this "when does Firefox alert for breached sites? [blog.mozilla.org...]