The fourth beta of Firefox 4 will be hitting on Monday, and notable will be the inclusion of hardware acceleration for Windows users that have the hardware and software to support Direct2D.
Firefox using your GPU to render won't be on by default – at least not yet. Mozilla's VP of engineering tweeted that Direct2D will be included in beta 4, but it isn't quite ready for everyone to be running it yet. Instead, the feature will be enabled through user intervention by modifying the config.
Mozilla details in its Wiki of how to turn it on and what to look out for:
D2D status: Direct2D is not turned on by default for Firefox 4 beta 4. (We weren't confident enough to turn it on for all users.) However, all the code in Firefox 4 beta 4, and it should work reasonably well for everyone. We really need testers, both on the beta and on nightlies. (We plan to enable Direct2D in nightlies as soon as beta 4 is tagged and branched.) To turn on Direct2D: Go in to about:config and set mozilla.widget.render-mode to 6, and gfx.font_rendering.directwrite.enabled to true. To turn off Direct2D, once it is on by default, set mozilla.widget.render-mode to 0. To check whether you are running with Direct2D, go to about:support and look at the bottom. (Once bug 586046 lands, there will be even more information about your graphics card in there.) Please look out for memory usage, rendering speed, and any rendering problems you might see. Also focus on interactions with plugins like Flash.
Firefox beta 4 will also bring with it the first official implementation of Tab Candy, the super slick way of managing lots of tabs.
While we hate it when the weekend ends, we're excited to try the new Firefox beta 4 that'll work our GPUs.