From Admininstrator account, open Firefox > Help > Check for Updates.
Other option:
Download v1.5.0.12: http://www.mozilla.com/en-US/firefox/all-older.html
All users are strongly encouraged to upgrade to Firefox 2.
Download v2.0.0.4: http://www.mozilla.com/en-US/firefox/all.html
Known Vulnerabilities in Mozilla Products
Brian Krebs, The Washington Post. “A New Vector For Hackers — Firefox Add-Ons”
