Since version 3.5 of Firefox has been enabled by default the management of color profiles of the images thus making things much easier for those who perhaps before did not bother to play with the appropriate browser configuration.
To oversimplify the concept, we can reduce it all by saying that each image is composed of the color information of each pixel, but this information defines an ideal color, and each monitor that color plays in their own way depending on the type and specifications of construction. When I go to save a photo to be published on the web I apply the color profile describing the browser in this case, how to show the different shades of color monitors.
For regular users say that using Firefox (or Safari if you use a Mac) is a step forward in the display of images in a manner as close as possible to what I visualize, then obviously if the monitor is not calibrated to introduce color casts, and if it is the difference will be smaller but will still be visible … at least this is what they say!