--- a/layout/painting/nsCSSRenderingBorders.h
+++ b/layout/painting/nsCSSRenderingBorders.h
@@ -141,18 +141,20 @@ private:
   Rect mOuterRect;
   Rect mInnerRect;
 
   // the style and size of the border
   uint8_t mBorderStyles[4];
   Float mBorderWidths[4];
   RectCornerRadii mBorderRadii;
 
-  // colors
+  // the colors for 'border-top-color' et. al.
   nscolor mBorderColors[4];
+
+  // the lists of colors for '-moz-border-top-colors' et. al.
   nsBorderColors* mCompositeColors[4];
 
   // the background color
   nscolor mBackgroundColor;
 
   // calculated values
   bool mOneUnitBorder;
   bool mNoBorderRadius;