--- a/layout/style/nsComputedDOMStyle.cpp
+++ b/layout/style/nsComputedDOMStyle.cpp
@@ -6433,17 +6433,31 @@ nsComputedDOMStyle::CreatePrimitiveValue
     RefPtr<CSSValue> shadowValue =
       GetCSSShadowArray(aStyleFilter.GetDropShadow(),
                         StyleColor()->mColor,
                         false);
     ErrorResult dummy;
     shadowValue->GetCssText(argumentString, dummy);
   } else {
     // Filter function argument.
-    SetCssTextToCoord(argumentString, aStyleFilter.GetFilterParameter());
+    if (aStyleFilter.GetType() == NS_STYLE_FILTER_BRIGHTNESS ||
+        aStyleFilter.GetType() == NS_STYLE_FILTER_CONTRAST ||
+        aStyleFilter.GetType() == NS_STYLE_FILTER_GRAYSCALE ||
+        aStyleFilter.GetType() == NS_STYLE_FILTER_INVERT ||
+        aStyleFilter.GetType() == NS_STYLE_FILTER_OPACITY ||
+        aStyleFilter.GetType() == NS_STYLE_FILTER_SATURATE ||
+        aStyleFilter.GetType() == NS_STYLE_FILTER_SEPIA) {
+      // Serialize <number-percentage> to number value.
+      RefPtr<nsROCSSPrimitiveValue> val = new nsROCSSPrimitiveValue;
+      val->SetNumber(
+        aStyleFilter.GetFilterParameter().GetFactorOrPercentValue());
+      val->GetCssText(argumentString);
+    } else {
+      SetCssTextToCoord(argumentString, aStyleFilter.GetFilterParameter());
+    }
   }
   filterFunctionString.Append(argumentString);
 
   // Filter function closing parenthesis.
   filterFunctionString.Append(')');
 
   value->SetString(filterFunctionString);
   return value.forget();