"Hardware Acceleration" (GPU Rendering) is one of the newly introduced feature of Mozilla Firefox 4.0. It was introduced to increase performance but some Firefox users might want to disable it as the text might not look well on their screens.
If you also want to disable Hardware Acceleration feature in Firefox, following trick will help you:
1. Open Mozilla Firefox, click on the orange Firefox button and select "Options".
2. Go to "Advanced" tab and disable "Use hardware acceleration when available" option.
3. Click on OK button and restart the browser.