SmartWare tested Firefox 2.0 and Internet Explorer 7.0's phising filters. They found that Firefox blocked 243 phishing sites that IE7 overlooked, while IE7 blocked 117 sites that Firefox didn't block.
Before I go any further with the numbers, I think it's important to offer a little background on how the phish-filtering technology is set up within both browsers. With IE7, the user is asked upon installation whether he wants to allow the browser to auto-check all Web sites against a Microsoft database. (More about how this technology works in IE7 is online here, and the obvious privacy issues are discussed here.)
Firefox's default setting, in contrast, uses a blacklist of known phishing sites that is stored on the user's computer and updated approximately every 30 minutes. Alternatively, Firefox users can opt to turn auto-detect on, in which case the browser will check Web sites the user visits by checking them against a database maintained by Google. (More about the service is online here.)