Report: Firefox had 115 security flaws reported in 2008 for Firefox, almost four times as many as other popular browsers. In contrast, 31 vulnerabilities were reported for versions of Microsoft’s Internet Explorer, while Opera and Safari claimed at least 30 and 32 reported security holes in 2008. Microsoft and Mozilla responded to vulnerabilities that the companies were notified about at the same time as the rest of the world. In 2007, Security Fix published an analysis which found that for a total of 284 days in 2006, exploit code for at least 10 “critical” flaws in IE was made publicly available online before Microsoft was able to ship updates.”]
Source: http://voices.washingtonpost.com/securityfix/2009/03/fanning_the_flames_of_the_brow.html