The symptom of my problem is that the same hex color in a PNG image does not match the CSS-defined color defined by the same hex code.
This problem only happens in Firefox when
gfx.color_management.mode is set to
2 (tagged images only) rather than
0 (off). (Firefox ICC color correction described here).
The image is http://dzfk93w6juz0e.cloudfront.net/images/background-top-light.png which at the bottom has the color
#c8e8bd. However, the shade of green is different to that color when Firefox color calibration is enabled.
Is this image inadvertently "tagged" for color correction?