Not goodFirefox 2's Phishing Protection feature was developed from the Google Safe Browsing feature of the Google Toolbar for Firefox using code donated by the search giant. By default, the Phishing Protection feature checks every page you visit against a local blacklist of known phishing sites and displays a warning if the site is fraudulent. This list is periodically updated by Firefox while the feature is enabled.
For more real-time protection, users can choose (from the Security panel of the Options/Preferences window) to send details of every site they visit to a remote service for checking (currently Google is the only service provider, though other phishing data providers can be supported). With this feature enabled, the URL of every page visited is sent to Google for checking over a secure connection. In addition, details of how users respond to phishing warnings are also sent. While real-time checking can offer greater protection, there are obvious privacy implications, which is why only the local list is enabled by default.
http://www.threadwatch.org/node/9531