Use hardware acceleration when available: If this option is ticked, Firefox will use Hardware Acceleration wherever possible to improve the speed with which pages are displayed. This means Firefox will utilize your GPU (graphics card), if you have one, instead of your CPU, to speed up page rendering. Windows Vista/7/8 benefits more fully from hardware acceleration than Windows XP, as under Vista/7/8 both Direct2D and Direct3D acceleration are enabled. Note that altering this setting requires a full restart of Firefox before the change is implemented.
To check the status of hardware acceleration in Firefox at any time, type About
:Support into the Address Bar and press Enter. Then check the 'gfx.direct2d.disabled' field, and the 'DirectWrite Enabled' field - these will say True if hardware acceleration is enabled, and False if it is not. The 'GPU Accelerated Windows' field will show '1/1 Direct3D 10' or '1/1 Direct3D 9' depending on the level of Direct3D support when hardware acceleration is enabled, or '0/1 Basic' if Direct3D acceleration is disabled. To test and compare your actual hardware acceleration performance after making any changes, first exit and restart Firefox, then run this test to see how many Frames Per Second (FPS) you get with and without hardware acceleration.
An unfortunate side-effect of enabling hardware acceleration in Firefox is that the text rendering method changes to one which some users may find displeasing. Fonts may appear blurry, overly thin, oddly spaced or inconsistently rendered across various sites. The easiest way to fix this issue is to disable hardware acceleration and restart Firefox - text rendering will now revert back to its original and familiar look. A slightly better method of fixing this issue is to keep the hardware acceleration option ticked, but set the gfx.direct2d.disabled preference to True - see the Advanced Tweaking section for details. This disables Direct2D acceleration while keeping Direct3D acceleration enabled. Another alternative is to keep the hardware acceleration option ticked, and install the Anti-Aliasing Tuner add-on, which allows customization of font appearance, while keeping the full advantages of hardware acceleration. Open the Options for this add-on (under Firefox menu button>Add-ons>Extensions), and try this suggested configuration: set Anti-Aliasing mode to ClearType and Rendering Mode to 'Natural Symmetric' for both text sizes, then tick all the 'ClearType Level' and 'Enhanced Contrast' boxes and set them to 100%. This will not be ideal, but you can experiment further to see if you can further customize text appearance to suit your taste.
Another aspect to consider regarding hardware acceleration is that disabling it may actually provide the best overall performance and stability in Firefox. With hardware acceleration enabled, the GPU will continually cycle between 2D and 3D clock speeds, and there may be periodic stuttering/pauses on certain pages, such as those with Flash video or heavy scripting. This is neither good for the GPU, nor good for smoothness. Enabling hardware acceleration can also result in Firefox crashes. Therefore I recommend experimenting with disabling hardware acceleration to see if it improves your browsing experience.