devtty writes with some bad news for Linux users, from OSNews: "The release notes for Firefox 4.0 beta 9 noted that it comes with hardware acceleration for Windows 7 and Vista via a combination of Direct2D, DirectX 9 and DirectX 10. Windows XP users will also enjoy hardware acceleration for many operations 'using our new Layers infrastructure along with DX9.' Furthermore, Mac OS X has excellent OpenGL support, they claim, so they've got that covered as well. No mention of Linux, and there's a reason for that. 'We tried enabling OpenGL on Linux, and discovered that most Linux drivers are so disastrously buggy (think "crash the X server at the drop of a hat, and paint incorrectly the rest of the time" buggy) that we had to disable it for now,' explains Zbarsky, 'Heck, we're even disabling WebGL for most Linux drivers, last I checked...'"
An update to the story softens this news slightly, saying that "hardware acceleration (OpenGL only) on Linux has been implemented, but due to bugs and issues, only one driver so far has been whitelisted (the proprietary NVIDIA driver)."