Firefox 3.5+ on the Mac cannot automatically detect what monitor profile you are using and just assumes the profile is sRGB. So even though Firefox 3.5+ does Color Correction correctly, it won’t work correctly because it doesn’t know what the profile your monitor is.
Here is an example:
In order to get things working right you have to tell Firefox where the correct profile is. To do that you have to enter “about:config” in the location bar. Then set:
gfx.color_management.mode to 1
gfx.color_management.display_profile to the location where your profile is.
Your profile is either here: /Library/ColorSync/Profiles/Displays/
or: /Users/[username]/Library/ColorSync