speeding up the display of web pages. Acceleration is only enabled for certain graphics hardware and drivers. One of the performance optimizations was moving all application data into a single file, omni.jar, using a new file format based on the Java Archive format(previous versions used multiple files in the Java Archive format). For later versions the file was renamed omni.ja. Privacy Firefox 4 contains support for the "do not track" header, an emerging standard for Web privacy. The header signals the user's request to the web service that any web visitor tracking service be disabled. In the future, this privacy request may become a legal requirement. It also introduced the ability to delete flash cookies, subjecting them to the same deletion rules as ordinary HTTP cookies. Development Nightly builds were marked as 4.0a1pre between February and June 2008, but were renamed to 3.1a1pre afterwards. Timeline Reception On 22 March 2011, and during the 24-hour launch period, Firefox 4 received 7.1 million downloads, as counted and verified by the Mozilla Foundation. Before that date, 3 million people downloaded the second release candidate of the browser, which later became the final version. As a result, the new version of the browser received 10 million downloads on the first day. Notwithstanding, it fell behind the previous record established by the launch of Firefox 3 in 2008, which was 8 million. Second-day downloads for the browser were reported to be 8.75 million, but the lack of an official representative from Guinness to monitor the numbers, made the record attained by Firefox 3 only unofficially been broken. Usage share 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%, 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. Also, at launch, Mozilla prompted existing customers to upgrade their browsers to the newer version, something Microsoft hadn't applied to users of older versions of Internet Explorer. Instead, Microsoft prompted users to upgrade via Windows Update several weeks after launch. On March 26, 2011, Firefox 4's usage share exceeded that of the 10-year-old and discontinued