For the brave and the bold, Mozilla has released the first public beta of its upcoming Firefox 4 web browser. The new browser, a 20.2 megabyte download (courtesy of VersionTracker), incorporates the following fixes and changes:

- Tabs are now on top by default on Windows only – Mac OS X and Linux will be changing when the theme has been modified to support the change.

- On Windows Vista and Windows 7 the menu bar has been replaced with the Firefox button.

- You can search for and switch to already open tabs in the Smart Location Bar

- New Addons Manager and extension management API (UI will be changed before final release)
Significant API improvements are available for JS-ctypes, a foreign function interface for extensions.

- The stop and reload buttons have been merged into a single button on Windows, Mac and Linux.

- The Bookmarks Toolbar has been replaced with a Bookmarks Button by default (you can switch it back if you’d like).

- Crash protection for Windows, Linux, and Mac when there is a crash in the Adobe Flash, Apple Quicktime or Microsoft Silverlight plugins.

- CSS Transitions are partially supported.

- Full WebGL support is included but disabled by default at this time.

- Core Animation rendering model for plugins on Mac OS X. Plugins which also support this rendering model can now draw faster and more efficiently.

- Native support for the HD HTML5 WebM video format.

- An experimental Direct2D rendering backend is available on Windows, turned off by default.

- Web developers can use Websockets for a low complexity, low latency, bidirectional communications API.

- Web developers can update the URL field without reloading the page using HTML History APIs.

- More responsive page rendering using lazy frame construction.

- Link history lookup is done asynchronously to provide better responsiveness during pageload.

- CSS :visited selectors have been changed to block websites from being able to check a user’s browsing history.

- New HTML5 parser.

- Support for more HTML5 form controls.

The Firefox 4 beta is available for free and requires Mac OS X 10.4 or later to install and run.

If you’ve tried it and have any feedback to offer, let us know in the comments