Firefox 3 supports color profiles, but you have to turn this setting on manually. There are some great blog posts that describe this in detail, which you should read for more information, but this "feature" greatly improves the accuracy of the colors.
Color profiles provide a kind of map for your computer about what colors in an image should look like. Your camera, monitor and printer all have color profiles. The color profile of a image will allow your printer and monitor to accurately render the colors of an image by mapping the image colors to the profile of your printer or monitor.