Mozilla 1.1 and earlier, and Mozilla-based browsers such as Netscape and Galeon, set the document referrer too quickly in certain situations when a new page is being loaded, which allows web pages to determine the next page that is being visited, including manually entered URLs, using the onunload handler.

Mozilla before 1.7, Firefox before 0.9, and Thunderbird before 0.7 allows remote attackers to determine the location of files on a user's hard drive by obscuring a file upload control and tricking the user into dragging text into that control.

Mozilla before 1.6 does not display the entire URL in the status bar when a link contains %00, which could allow remote attackers to trick users into clicking on unknown or untrusted sites and facilitate phishing attacks.

Firefox before 1.0 and Mozilla before 1.7.5 display the SSL lock icon when an insecure page loads a binary file from a trusted site, which could facilitate phishing attacks.