However, if you have a low-end graphics card, sometimes, it can make problems when watching videos online, play games, etc. so you may need to disable hardware acceleration.
In Firefox 4 hardware acceleration is enabled by default. If you find any issues, you can disable it very easily from the option menu.
Run Firefox web browser and go to Option - Advance. In the General tab, un-check the box labeled Use hardware acceleration when available and save the settings by clicking the OK button.