Many changes were made to the user interface. By default, tabs were displayed on the top of the window, above the location bar in the area formerly occupied by the window's title bar. The "stop", "reload", and "go" buttons were combined into a single button, placed on the right side of the address bar. The button changed dynamically, based on the current state of the page. On Windows Vista and Windows 7, the menu bar is hidden by default with the most common actions moved to a new "Firefox" menu in the upper left-hand corner of the browser. Users can create persistent "app tabs", and customize the tab bar, as well as the bookmark and navigation bars. Many of these features are similar to ones introduced by Google Chrome. Engine Firefox 4 is based on the Gecko 2.0 engine, which adds and improves support for HTML5, CSS3, WebM, and WebGL. Also, it includes a new JavaScript engine (JägerMonkey) and better XPCOM APIs. JägerMonkey is a new JavaScript engine designed to work alongside the TraceMonkey engine introduced with Firefox 3.5. It improves performance by compiling "non-traceable" JavaScript into machine language for faster execution. Firefox 4 is the first version of Firefox to drop native support of the Gopher protocol; however, continued support is available through an add-on. Firefox 4 introduces an audio API, which provides a way to programmatically access or create audio data associated with an HTML5 audio element. It allows, for example, to visualize raw sound data, to use filters or to show the audio spectrum. Firefox 4 no longer relies on the underlying OS for text layout/shaping. Instead, it uses HarfBuzz. This allows for smart OpenType layout/shaping which is consistent across different operating systems. Performance Firefox 4 has marked a major change in performance in comparison to former versions 3.6 and 3.5. The browser has made significant progress in Sunspider JavaScript tests as well as improvements in supporting HTML5. Since Firefox 4.0 Beta 5, hardware acceleration of content is enabled by default on Windows Vista and Windows 7 machines using Direct2D, on OS X using Quartz (basically CPU-only), and Linux using XRender. Hardware acceleration of compositing is enabled by default on Windows XP, Windows Vista and Windows 7 machines using Direct3D, OS X and Linux using OpenGL. Using hardware acceleration allows the browser to tap into the computer's graphics processing unit, lifting the burden from the CPU and