When Firefox detects that a saved login may have been exposed in a known data breach, it shows a clear, private alert in your Firefox Password Manager. These alerts help you stay safe online by guiding you to change your password before anyone can misuse your account. Firefox uses secure, anonymous checks and never sends your saved passwords or login information to anyone—not even to Mozilla.
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How Firefox notifies about website breaches
Firefox checks the date of a known website breach against the date you saved a password for that website. If the website was breached after you saved your password, you’ll see this alert.
Vulnerable Password: This password has been used on another account that was likely in a data breach. Reusing credentials puts all your accounts at risk. Change this password. Go to (name of the site).
What the alert means
- A website where you have a saved login experienced a known data breach.
- Your saved password for that site may no longer be secure.
- Firefox helps you act quickly by flagging the login and guiding you to update it.
Firefox will also check to see if you’ve reused any of these potentially vulnerable passwords with other logins you’ve saved to Firefox. The browser does this by creating an encrypted list of your breached passwords, then checking it against all saved passwords. Firefox does not keep logs of your plaintext passwords or know them.
Turn off website breach alerts
Disabling the feature also prevents Firefox from checking to see if you’ve reused these potentially vulnerable passwords on any of your other saved logins.
- In the Menu bar at the top of the screen, click and select (or , in some cases).Click the menu button
and select .
- Select the panel on the left.
- Scroll down to the Passwords section.
- Deselect the checkbox for Show alerts about passwords for breached websites.
Check if your email was in a breach
You can also use Mozilla Monitor to check if your email address appeared in any known data breaches. Just enter your email, and you’ll get a private report. It’s free and secure.