If you are using Windows Vista or 7, text in Firefox may appear blurry or pixelated. This is usually due to Windows ClearType not being turned on. This article will explain how to enable it.
The text in Firefox should now look good.
Some computers run slower with ClearType turned on. If you are using Windows 7, you may be able to improve your computer's performance by installing the following updates from Microsoft.com:
These recommended updates can be installed using Windows Update. If you need help with Windows Update, see Microsoft's article Install Windows updates in Windows 7 .
It's possible that you are also experiencing issues related to outdated graphics card drivers. See Upgrade your graphics drivers to use hardware acceleration and WebGL for more information, including how to disable hardware acceleration in Firefox as a possible workaround.