Another thing you can try is this ...
http://support.mozilla.com/en-US/questions/751988
This involves you turning off hardware acceleration in the web browser, which is currently known to cause some blurry text problems with certain graphics cards/drivers for graphics cards.
Also if you are using an ATI/AMD graphics card that supports morphological filtering in the drivers, turn that feature off that also is known to cause blurry text on web pages, applications and games. Use the standard Anti-Aliasing in the drivers and set it to application settings (so that way each application controls what it needs).
I also advise you update your graphics drivers for your graphics card, there has been so many recent changes in graphics card technology recently and video graphics drivers for new features added to applications that can use the graphics card to help accelerate computer performance (GPU acceleration/GPU computing. This is why you are starting to see many common applications like web browsers take advantage of the graphics cards power and to help the CPU (Processor) speed up applications, but all these new fetures will not work if the graphics cards drivers are out dated and this is why you maybe seeing these strange things currently like blurry text.
Things you may like to read regarding this new feature "Hardware acceleration in Firefox".
http://hacks.mozilla.org/2010/09/hardware-acceleration/
http://blog.mozilla.com/joe/2010/05/25/hardware-accelerating-firefox/
http://www.basschouten.com/blog1.php/2010/03/02/presenting-direct2d-hardware-acceleratio
Remember if you are still using Windows XP some of the features will not work, like Direct2D..
http://www.flirt4free.com/
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