It isn't available from the official Firefox website yet, but Firefox 4 is now available to download from the Mozilla releases FTP server. Update: you can hit a random FTP mirror by using these links: Windows / Mac OS X / Linux. .

Firefox 4 brings with it a bunch of new features, including,  a completely new user interface that makes it look a lot like Chrome. Hardware acceleration and the jet-powered JaegerMonkey JavaScript engine are the next two biggies. In true Mozilla style, Firefox 4 also brings support for many emerging standards, such as HTML5, CSS3 and WebGL. Finally, there's neat features like built-in Sync and workspace management with Panorama.