Firefox to US$7,500 cash reward) to researchers who discover severe security holes in Firefox. Official guidelines for handling security vulnerabilities discourage early disclosure of vulnerabilities so as not to give potential attackers an advantage in creating exploits. Because Firefox generally has fewer publicly known security vulnerabilities than Internet Explorer (see "Comparison of web browsers"), improved security is often cited as a reason to switch from Internet Explorer to Firefox. "The Washington Post" reported that exploit code for known critical security vulnerabilities in Internet Explorer was available for 284 days in 2006. In comparison, exploit code for known, critical security vulnerabilities in
Firefox 3.5 to support X BitMap images. Estimates of Firefox 3.5's global market share in February 2010 were around 15–20% and rose rapidly in July 2009 as users migrated from Firefox 3.0. From January 2010 it began to decline as users migrated to Firefox 3.6. Between mid-December 2009 and February 2010, Firefox 3.5 was the most popular browser (when counting individual browser versions) according to StatCounter, and was one of the top 3 browser versions according to Net Applications. Both milestones involved passing Internet Explorer 7, which previously held the No. 1 and No. 3 spots in popularity according to StatCounter and