On the official launch date, the usage share for the Firefox 4 was 1.95%, which was 0.34% higher than the previous day according to analytics website StatCounter. As a comparison, the usage share for the Internet Explorer 9 on March 22 was 0.87%,[56] and it was released the prior week, on March 14. A potential factor on Firefox 4's higher usage share is that the latter supports both Windows 2000 and XP, two operating systems Internet Explorer 9 does not support.