--- a/layout/style/nsCSSParser.cpp
+++ b/layout/style/nsCSSParser.cpp
@@ -6756,16 +6756,19 @@ CSSParserImpl::ParseColor(nsCSSValue& aV
         }
         aValue.SetIntegerColorValue(rgba, unit);
         return CSSParseResult::Ok;
       }
       break;
 
     case eCSSToken_Ident: {
       if (NS_ColorNameToRGB(tk->mIdent, &rgba)) {
+        // Lowercase color name, since keyword values should be
+        // serialized in lowercase.
+        nsContentUtils::ASCIIToLower(tk->mIdent);
         aValue.SetStringValue(tk->mIdent, eCSSUnit_Ident);
         return CSSParseResult::Ok;
       }
       nsCSSKeyword keyword = nsCSSKeywords::LookupKeyword(tk->mIdent);
       if (Maybe<int32_t> value = GetEnumColorValue(keyword, mIsChrome)) {
         aValue.SetIntValue(value.value(), eCSSUnit_EnumColor);
         return CSSParseResult::Ok;
       }

--- a/layout/style/test/chrome/test_author_specified_style.html
+++ b/layout/style/test/chrome/test_author_specified_style.html
@@ -5,17 +5,17 @@
 <script>
 var values = [
   // specified value         // returned from getAuthoredPropertyValue()
   "#12F",                    "#12f",
   "#1122FF",                 "#1122ff",
   "rgb(10,20,30)",           "rgb(10, 20, 30)",
   "Rgb(300,20,30)",          "rgb(255, 20, 30)",
   "rgba(10,20,30,0.250)",    "rgba(10, 20, 30, 0.25)",
-  "OrangeRed",               "OrangeRed",
+  "OrangeRed",               "orangered",
   "rgb(10%,25%,99%)",        "rgb(10%, 25%, 99%)",
   "rgb(6.66667%,0%,0.0%)",   "rgb(6.66667%, 0%, 0%)",
   "HSL(0,25%,75%)",          "hsl(0, 25%, 75%)",
   "hsl(60,0%,0%)",           "hsl(60, 0%, 0%)",
   "hsla(60,50%,50%,0.1250)", "hsla(60, 50%, 50%, 0.125)",
   "rgba(0,0,0,0)",           "rgba(0, 0, 0, 0)",
   "rgba(50,50,50,1)",        "rgb(50, 50, 50)",
   "rgba(50%,50%,50%,1)",     "rgb(50%, 50%, 50%)",