FF3 has a large number of improvements to FF2, but a few of them have been auto disabled because of performance hits. Firstly is the improved color management system which, if turned on will make a performance hit of ~10%. Then again…if your on a modern computer with relatively good cpu and ram, I doubt you can see a difference. However…if you are like me and regularly open high res images that are enormous…proceed with caution.
Type about:config into the address bar.
Convince FF3 that you will be careful
type gfx.color_management.enabled into the filter field and change it to True.
Restart FF3, and you’ll get much better looking images.