Mozilla is planning on releasing Firefox beta 4 on Monday with two major new features: hardware-accelerated graphics for Windows users and tab sets, or better known as tab candy. Hardware-accelerated graphics done with Direct2D will not be turned on by default, as Mike Shaver, Mozilla's vice president of engineering, sent a tweet stating "b4 won't have D2D on by default after all; just not quite ready to send it to that many users. soon!"
If you wish to enable Direct2D rendering, you can follow Mozilla's instructions on their wiki, which consists of this:
Type "about:config" into the URL bar, type in "gfx.font" in the Filter box, set "gfx.font_rendering.directwrite.enabled" to true by double clicking. Then below that, right click and select New >> Integer, name it "mozilla.widget.render-mode" and set the value to 6 then restart the browser.
Code for Firefox 4 beta 4 is frozen and the release should be on Monday, August 23rd. A major goal for Mozilla for their next browser was speed. Enabling Direct2D hardware acceleration helps with the display of text and graphics, which if you follow the Internet Explorer 9 previews, Microsoft is already touting that feature and speed of their next browser.
Mozilla also had the goal of ultimate user friendliness by implementing tab sets, or as it was called early on, tab candy. Tab sets allow you to group your tabs together into different sets, such as "Work", "Research", "School", "Home", or anything you wish.
Firefox users will be able to look forward to one more beta after this which should be the last with new features. That beta will also consist of fixing any bugs that Mozilla has found along the way.