Final build for Mozilla's major update of their web-browser Firefox 4 will officially get revealed on 22 March, but as expected the build had already made it's way to Mozilla's official FTP servers and can be downloaded right now.

For users with the older version of the web-browser, Firefox 4 brings in lots of new features, the most notable being a completely revamped new streamlined user interface, enhanced performance, support for newest open Web technologies, hardware acceleration, jet-powered JaegerMonkey JavaScript engine, built-in Sync, restartless add-ons, and Panorama workspace management.

Firefox 4 Performance Improvements

Firefox 4 New Tab Structure

Firefox 4 New Compact Menu

What’s New in this Firefox 4 :

• Blacklisted a few invalid HTTPS certificates
• Updated localizations for 29 locales
• Added Vietnamese localization, bringing the total languages available in Firefox 4 to 83

As well as these features from previous Firefox 4 Betas:

• Support for the proposed Do Not Track ("DNT") header
• Connection status messages are now shown in a small overlay
• WebGL is enabled on all platforms, but, like for other hardware acceleration features, many buggy drivers or driver versions are blocked
• The default homepage design has been refreshed
• Firefox no longer switches into offline mode automatically
• Overhaul of the bookmarks and history code, enabling faster bookmarking and startup performance
• Per-compartment garbage collection is now enabled, reducing work done during complex animations
• The Firefox Sync setup experience has been greatly improved across desktop and mobile devices
• Additional polish for the Firefox Add-ons Manager
• Uses JägerMonkey, a new, faster JavaScript engine
• Certain rendering operations are now hardware-accelerated using Direct3D 9 on Windows XP, Direct3D 10 on Windows Vista and 7, and OpenGL on Mac OS X
• Improved web typography using OpenType with support for ligatures, kerning and font variants
• HTML5 Forms API makes web based forms easier to implement and validate
• Support for the new proposed Audio Data API
• Direct2D Hardware Acceleration is now on by default for Windows 7 users
• Firefox button has a new look for Windows Vista and Windows 7 users
• Support for HSTS security protocol allowing sites to insist that they only be loaded over SSL
• Firefox Sync is now included by default
• A new feature gives users a visual overview of all open tabs, allowing them to be sorted and grouped
• An experimental API is included to provide more efficient Javascript animations
• Firefox now supports the HTML5 video "buffered" property
• Tabs are now on top by default on Windows, Mac OS X, and Linux
• You can turn any tab into an "App Tab" by right-clicking on it and selecting "Make into App Tab" from the context menu
• Web developers can animate content using CSS Transitions
• Responsiveness and scrolling improvements from the new retained layers layout system
• JavaScript speed improvements due to engine optimizations
• Changes to how XPCOM components are registered in order to help startup time and process separation
• 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 OS X, 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 OS X 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
• 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
• 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
• Web authors can now get touch events from Firefox users on Windows 7 machines
• A new way of representing values in JavaScript that allows Firefox to execute heavy, numeric code (used for things like graphics and animations) more efficiently

Developers can find out about all the changes and
new features at the Mozilla Developer Center.

Although, Mozilla has told DownloadSquad that this might not turn out to be the actual final build as it is still under-going through final quality-assurance checks - users can still install this which will automatically update if a newer build is released.