Mozilla has released the first Beta of Firefox 4, the next major version of the popular web browser. Apart from the new 'Chromified' tabs-on-top UI, there are many major improvements in performance and HTML5 support. This release also adds support for the new WebM video format. Other changes include faster DOM and CSS performance, improved UI responsiveness, hardware 2D acceleration, experimental WebGL support, and better JavaScript performance (though this beta does not include the new JaegerMonkey JIT engine). More details on the Mozilla blog.