URL: http://www.us-cert.gov/cas/techalerts/TA07-151A.html

Mozilla has released new versions of Firefox, Thunderbird, and SeaMonkey to address several vulnerabilities. Further details about these vulnerabilities are available from Mozilla and the Vulnerability Notes Database. An attacker could exploit these vulnerabilities by convincing a user to view a specially-crafted HTML document, such as a web page or an HTML email message.

Support for Firefox 1.5 is scheduled to end in June 2007. According to Mozilla:

Firefox 1.5.0.x will be maintained with security and stability updates until June 2007. All users are strongly encouraged to upgrade to Firefox 2.