Firefox's phishing and malware site protection uses lists from the SafeBrowsing project, which is managed by Google. You can submit a URL of a phishing page using the Help menu. Either: menu button > Help > Report deceptive site...

A malicious website is any website that's been designed to cause harm. In this article, we'll focus on phishing websites and malware websites. A phishing website – sometimes called a “spoof” or “lookalike” website – steals your data. Phishing websites look like legitimate websites.

What happens when a page is blocked? Firefox will block the page from loading and display a Deceptive Site warning for phishing sites, Reported Unwanted Software Page for unwanted software sites and Reported Attack Page for malware sites.

ReportFraud.ftc.gov.