--- a/layout/style/nsCSSValue.cpp
+++ b/layout/style/nsCSSValue.cpp
@@ -3181,20 +3181,20 @@ nsCSSValueFloatColor::GetColorValue(nsCS
   MOZ_ASSERT(nsCSSValue::IsFloatColorUnit(aUnit), "unexpected unit");
 
   // We should clamp each component value since eCSSUnit_PercentageRGBColor
   // and eCSSUnit_PercentageRGBAColor may store values greater than 1.0.
   if (aUnit == eCSSUnit_PercentageRGBColor ||
       aUnit == eCSSUnit_PercentageRGBAColor) {
     return NS_RGBA(
       // We need to clamp before multiplying by 255.0f to avoid overflow.
-      NSToIntRound(mozilla::clamped(mComponent1, 0.0f, 1.0f) * 255.0f),
-      NSToIntRound(mozilla::clamped(mComponent2, 0.0f, 1.0f) * 255.0f),
-      NSToIntRound(mozilla::clamped(mComponent3, 0.0f, 1.0f) * 255.0f),
-      NSToIntRound(mozilla::clamped(mAlpha, 0.0f, 1.0f) * 255.0f));
+      mozilla::clamped(NSToIntFloor(mComponent1 * 256.0f), 0, 255),
+      mozilla::clamped(NSToIntFloor(mComponent2 * 256.0f), 0, 255),
+      mozilla::clamped(NSToIntFloor(mComponent3 * 256.0f), 0, 255),
+      mozilla::clamped(NSToIntFloor(mAlpha * 256.0f), 0, 255));
   }
 
   // HSL color
   MOZ_ASSERT(aUnit == eCSSUnit_HSLColor ||
              aUnit == eCSSUnit_HSLAColor);
   nscolor hsl = NS_HSL2RGB(mComponent1, mComponent2, mComponent3);
   return NS_RGBA(NS_GET_R(hsl),
                  NS_GET_G(hsl),