Firefox / Webkit / IE / Opera look consistent with me in terms of the template they display, i.e. darker color on the outer side of the border - on the left and on the border, and a lighter color on the outer border of the border -right and border-bottom.
Actual colors seem to vary for each browser. In your example:
Opera
Darker: # 7f0000; RGB (127.0.0)
Lighter: # c04141; RGB (192.65.65)
Firefox
Darker: # 770000; RGB (119.0.0)
Lighter: # d47f7f; RGB (212127127)
Webkit
Darker: # 560000; RGB (86.0.0)
Lighter: # aa0000; RGB (170.0.0)
IE8
Darker: # 2e0303; RGB (46.3.3)
Lighter: # b80d0c; RGB (184,13,12)
Color factors are understandable, and Webkit seems to be the only logical one - the specified color for lighter and double the RGB value for darker.
The rest are completely different, but the template is at least the same.
source share