As we await the final version of Firefox 3, Firefox 4 Pre-Alpha 1 (Minefield) is already available for download on Mozilla’s FTP server. This is a 'launch' surprise and seems that it has been designed to get attention that the Internet Explorer 8 Beta 1 already have.
The download is available for Linux and Windows as a package and installer. That does not alter the current efforts to focus on completing the version 3 of which should be launched before the summer.Without that still have clear objectives, rumors abound that Firefox 4 will be built from scratch, focusing on improving the performance-weak point so far-reaching and could not be consistent with the themes and extensions today.[via]