The director of Product Platform Management, Christopher Blizzard emphasised that Firefox 4 supports complete hardware acceleration under Windows 7 and Windows Vista via a combination of Direct2D, DirectX 9 and DirectX 10. While IE9 wont be available to the Windows XP operating system, hardware acceleration is something that is being looked at for certain operations (DirectX 9) in Firefox. For Mac OS X, hardware acceleration is supported by OpenGL, qualified as excellent.
Strangely, Christopher Blizzard didn’t mince his words when talking about Linux, with questions being raised after comments were left on user community sites, with Boris Zbarsky, a developer at Mozilla answering. "We have tried to activate OpenGL for Linux, and we have discovered that most of the Linux drivers are full of bugs which mean that we have had to disable the service for the moment". Adding that support for WebGL (for 3D Web) had also been disabled for most Linux drivers (this support is assured by Direct3D in Windows).
For Linux, hardware acceleration will be done by composition (via OpenGL) which creates some issues. Hardware acceleration for content provided XRender works well and effectively, "if your drivers are decent, you will have something similar to Direct2D", states Boris Zbarsky, who also used this opportunity to request help from X.Org developers.
As for full hardware acceleration under Linux for Firefox 4, Mozilla’s developers have nevertheless managed to have a stable environment with Nvidia proprietary drivers.