diff --git a/content/base/src/nsAttrValue.cpp b/content/base/src/nsAttrValue.cpp
index dd9b995358f..c372a1bfd4a 100644
--- a/content/base/src/nsAttrValue.cpp
+++ b/content/base/src/nsAttrValue.cpp
@@ -714,7 +714,7 @@ nsAttrValue::GetEnumString(nsAString& aResult, bool aRealTag) const
     if (table->value == val) {
       aResult.AssignASCII(table->tag);
       if (!aRealTag && allEnumBits & NS_ATTRVALUE_ENUMTABLE_VALUE_NEEDS_TO_UPPER) {
-        ToUpperCase(aResult);
+        nsContentUtils::ASCIIToUpper(aResult);
       }
       return;
     }
@@ -1316,7 +1316,7 @@ nsAttrValue::ParseEnumValue(const nsAString& aValue,
       if (!equals) {
         nsAutoString tag;
         tag.AssignASCII(tableEntry->tag);
-        ToUpperCase(tag);
+        nsContentUtils::ASCIIToUpper(tag);
         if ((equals = tag.Equals(aValue))) {
           value |= NS_ATTRVALUE_ENUMTABLE_VALUE_NEEDS_TO_UPPER;
         }
diff --git a/content/base/src/nsContentSink.cpp b/content/base/src/nsContentSink.cpp
index 601e7829c0c..768acbce10f 100644
--- a/content/base/src/nsContentSink.cpp
+++ b/content/base/src/nsContentSink.cpp
@@ -617,8 +617,9 @@ nsContentSink::ProcessLinkHeader(nsIContent* aElement,
             if (media.IsEmpty()) {
               media = value;
 
-              // HTML4.0 spec is inconsistent, make it case INSENSITIVE
-              ToLowerCase(media);
+              // The HTML5 spec is formulated in terms of the CSS3 spec,
+              // which specifies that media queries are case insensitive.
+              nsContentUtils::ASCIIToLower(media);
             }
           } else if (attr.LowerCaseEqualsLiteral("anchor")) {
             if (anchor.IsEmpty()) {
@@ -757,7 +758,7 @@ nsContentSink::ProcessMETATag(nsIContent* aContent)
     nsAutoString result;
     aContent->GetAttr(kNameSpaceID_None, nsGkAtoms::content, result);
     if (!result.IsEmpty()) {
-      ToLowerCase(header);
+      nsContentUtils::ASCIIToLower(header);
       nsCOMPtr<nsIAtom> fieldAtom(do_GetAtom(header));
       rv = ProcessHeaderData(fieldAtom, result, aContent); 
     }
@@ -769,7 +770,7 @@ nsContentSink::ProcessMETATag(nsIContent* aContent)
     nsAutoString result;
     aContent->GetAttr(kNameSpaceID_None, nsGkAtoms::content, result);
     if (!result.IsEmpty()) {
-      ToLowerCase(result);
+      nsContentUtils::ASCIIToLower(result);
       mDocument->SetHeaderData(nsGkAtoms::handheldFriendly, result);
     }
   }
diff --git a/content/base/src/nsDOMAttribute.cpp b/content/base/src/nsDOMAttribute.cpp
index 77795865214..6e8f52fe641 100644
--- a/content/base/src/nsDOMAttribute.cpp
+++ b/content/base/src/nsDOMAttribute.cpp
@@ -211,10 +211,9 @@ nsDOMAttribute::GetNameAtom(nsIContent* aContent)
       aContent->IsInHTMLDocument() &&
       aContent->IsHTML()) {
     nsAutoString name;
-    mNodeInfo->NameAtom()->ToString(name);
-    nsAutoString lower;
-    ToLowerCase(name, lower);
-    nsCOMPtr<nsIAtom> nameAtom = do_GetAtom(lower);
+    mNodeInfo->GetName(name);
+    nsContentUtils::ASCIIToLower(name);
+    nsCOMPtr<nsIAtom> nameAtom = do_GetAtom(name);
     nameAtom.swap(result);
   } else {
     nsCOMPtr<nsIAtom> nameAtom = mNodeInfo->NameAtom();
diff --git a/content/base/src/nsDOMAttributeMap.cpp b/content/base/src/nsDOMAttributeMap.cpp
index 6a6d442d643..f0617a0e5fa 100644
--- a/content/base/src/nsDOMAttributeMap.cpp
+++ b/content/base/src/nsDOMAttributeMap.cpp
@@ -335,9 +335,7 @@ nsDOMAttributeMap::SetNamedItemInternal(nsIDOMNode *aNode,
       else {
         if (mContent->IsInHTMLDocument() &&
             mContent->IsHTML()) {
-          nsAutoString lower;
-          ToLowerCase(name, lower);
-          name = lower;
+          nsContentUtils::ASCIIToLower(name);
         }
 
         rv = mContent->NodeInfo()->NodeInfoManager()->
diff --git a/content/base/src/nsDocument.cpp b/content/base/src/nsDocument.cpp
index 4837d14f621..b429d2f450a 100644
--- a/content/base/src/nsDocument.cpp
+++ b/content/base/src/nsDocument.cpp
@@ -4423,7 +4423,7 @@ nsDocument::CreateElement(const nsAString& aTagName,
   bool needsLowercase = IsHTML() && !IsLowercaseASCII(aTagName);
   nsAutoString lcTagName;
   if (needsLowercase) {
-    ToLowerCase(aTagName, lcTagName);
+    nsContentUtils::ASCIIToLower(aTagName, lcTagName);
   }
 
   rv = CreateElem(needsLowercase ? lcTagName : aTagName,
diff --git a/content/base/src/nsStyleLinkElement.cpp b/content/base/src/nsStyleLinkElement.cpp
index 9cb62d9cfd4..36e923811ba 100644
--- a/content/base/src/nsStyleLinkElement.cpp
+++ b/content/base/src/nsStyleLinkElement.cpp
@@ -185,7 +185,7 @@ PRUint32 nsStyleLinkElement::ParseLinkTypes(const nsAString& aTypes)
   while (current != done) {
     if (nsContentUtils::IsHTMLWhitespace(*current)) {
       if (inString) {
-        ToLowerCase(Substring(start, current), subString);
+        nsContentUtils::ASCIIToLower(Substring(start, current), subString);
         linkMask |= ToLinkMask(subString);
         inString = false;
       }
@@ -199,8 +199,8 @@ PRUint32 nsStyleLinkElement::ParseLinkTypes(const nsAString& aTypes)
     ++current;
   }
   if (inString) {
-    ToLowerCase(Substring(start, current), subString);
-     linkMask |= ToLinkMask(subString);
+    nsContentUtils::ASCIIToLower(Substring(start, current), subString);
+    linkMask |= ToLinkMask(subString);
   }
   return linkMask;
 }
diff --git a/content/html/content/src/nsGenericHTMLElement.cpp b/content/html/content/src/nsGenericHTMLElement.cpp
index 6fc86ebd7b7..0ef219ce376 100644
--- a/content/html/content/src/nsGenericHTMLElement.cpp
+++ b/content/html/content/src/nsGenericHTMLElement.cpp
@@ -2489,7 +2489,7 @@ nsresult
 nsGenericHTMLElement::SetContentEditable(const nsAString& aContentEditable)
 {
   nsString contentEditable;
-  ToLowerCase(aContentEditable, contentEditable);
+  nsContentUtils::ASCIIToLower(aContentEditable, contentEditable);
 
   if (contentEditable.EqualsLiteral("inherit")) {
     UnsetAttr(kNameSpaceID_None, nsGkAtoms::contenteditable, true);
diff --git a/content/html/content/src/nsHTMLLinkElement.cpp b/content/html/content/src/nsHTMLLinkElement.cpp
index 478f2cb840c..18ce3485e81 100644
--- a/content/html/content/src/nsHTMLLinkElement.cpp
+++ b/content/html/content/src/nsHTMLLinkElement.cpp
@@ -433,7 +433,9 @@ nsHTMLLinkElement::GetStyleSheetInfo(nsAString& aTitle,
   }
 
   GetAttr(kNameSpaceID_None, nsGkAtoms::media, aMedia);
-  ToLowerCase(aMedia); // HTML4.0 spec is inconsistent, make it case INSENSITIVE
+  // The HTML5 spec is formulated in terms of the CSSOM spec, which specifies
+  // that media queries should be ASCII lowercased during serialization.
+  nsContentUtils::ASCIIToLower(aMedia);
 
   nsAutoString mimeType;
   nsAutoString notUsed;
diff --git a/content/html/content/src/nsHTMLStyleElement.cpp b/content/html/content/src/nsHTMLStyleElement.cpp
index 935af2a8e60..8d87a269e56 100644
--- a/content/html/content/src/nsHTMLStyleElement.cpp
+++ b/content/html/content/src/nsHTMLStyleElement.cpp
@@ -340,7 +340,9 @@ nsHTMLStyleElement::GetStyleSheetInfo(nsAString& aTitle,
   aTitle.Assign(title);
 
   GetAttr(kNameSpaceID_None, nsGkAtoms::media, aMedia);
-  ToLowerCase(aMedia); // HTML4.0 spec is inconsistent, make it case INSENSITIVE
+  // The HTML5 spec is formulated in terms of the CSSOM spec, which specifies
+  // that media queries should be ASCII lowercased during serialization.
+  nsContentUtils::ASCIIToLower(aMedia);
 
   GetAttr(kNameSpaceID_None, nsGkAtoms::type, aType);
 
diff --git a/content/html/document/src/nsHTMLDocument.cpp b/content/html/document/src/nsHTMLDocument.cpp
index baf1d436ac9..42879425af3 100644
--- a/content/html/document/src/nsHTMLDocument.cpp
+++ b/content/html/document/src/nsHTMLDocument.cpp
@@ -1361,7 +1361,7 @@ nsHTMLDocument::Open(const nsAString& aContentTypeOrUrl,
   contentType.AssignLiteral("text/html");
   if (aOptionalArgCount > 0) {
     nsAutoString type;
-    ToLowerCase(aContentTypeOrUrl, type);
+    nsContentUtils::ASCIIToLower(aContentTypeOrUrl, type);
     nsCAutoString actualType, dummy;
     NS_ParseContentType(NS_ConvertUTF16toUTF8(type), actualType, dummy);
     if (!actualType.EqualsLiteral("text/html") &&
diff --git a/content/svg/content/src/nsSVGStyleElement.cpp b/content/svg/content/src/nsSVGStyleElement.cpp
index 181ef23b450..14204e643cc 100644
--- a/content/svg/content/src/nsSVGStyleElement.cpp
+++ b/content/svg/content/src/nsSVGStyleElement.cpp
@@ -337,9 +337,9 @@ nsSVGStyleElement::GetStyleSheetInfo(nsAString& aTitle,
   aTitle.Assign(title);
 
   GetAttr(kNameSpaceID_None, nsGkAtoms::media, aMedia);
-  // SVG spec refers to the HTML4.0 spec which is inconsistent, make it
-  // case INSENSITIVE
-  ToLowerCase(aMedia);
+  // The SVG spec is formulated in terms of the CSS2 spec,
+  // which specifies that media queries are case insensitive.
+  nsContentUtils::ASCIIToLower(aMedia);
 
   GetAttr(kNameSpaceID_None, nsGkAtoms::type, aType);
   if (aType.IsEmpty()) {
diff --git a/content/xbl/src/nsXBLPrototypeHandler.cpp b/content/xbl/src/nsXBLPrototypeHandler.cpp
index 017e762d020..0b2a36ad9f2 100644
--- a/content/xbl/src/nsXBLPrototypeHandler.cpp
+++ b/content/xbl/src/nsXBLPrototypeHandler.cpp
@@ -932,21 +932,18 @@ nsXBLPrototypeHandler::ConstructPrototype(nsIContent* aKeyElement,
   if (!key.IsEmpty()) {
     if (mKeyMask == 0)
       mKeyMask = cAllModifiers;
-    ToLowerCase(key);
+    nsContentUtils::ASCIIToLower(key);
 
     // We have a charcode.
     mMisc = 1;
     mDetail = key[0];
     const PRUint8 GTK2Modifiers = cShift | cControl | cShiftMask | cControlMask;
     if ((mKeyMask & GTK2Modifiers) == GTK2Modifiers &&
-        modifiers.First() != PRUnichar(',') &&
-        (mDetail == 'u' || mDetail == 'U'))
+        modifiers.First() != PRUnichar(',') && mDetail == 'u')
       ReportKeyConflict(key.get(), modifiers.get(), aKeyElement, "GTK2Conflict");
     const PRUint8 WinModifiers = cControl | cAlt | cControlMask | cAltMask;
     if ((mKeyMask & WinModifiers) == WinModifiers &&
-        modifiers.First() != PRUnichar(',') &&
-        (('A' <= mDetail && mDetail <= 'Z') ||
-         ('a' <= mDetail && mDetail <= 'z')))
+        modifiers.First() != PRUnichar(',') && ('a' <= mDetail && mDetail <= 'z'))
       ReportKeyConflict(key.get(), modifiers.get(), aKeyElement, "WinConflict");
   }
   else {
diff --git a/content/xslt/src/xslt/txMozillaXMLOutput.cpp b/content/xslt/src/xslt/txMozillaXMLOutput.cpp
index 172750139c6..000bd3494ba 100644
--- a/content/xslt/src/xslt/txMozillaXMLOutput.cpp
+++ b/content/xslt/src/xslt/txMozillaXMLOutput.cpp
@@ -160,7 +160,7 @@ txMozillaXMLOutput::attribute(nsIAtom* aPrefix,
 
     if (mOpenedElementIsHTML && aNsID == kNameSpaceID_None) {
         nsAutoString lnameStr;
-        ToLowerCase(aLocalName, lnameStr);
+        TX_ToLowerCase(aLocalName, lnameStr);
         lname = do_GetAtom(lnameStr);
     }
     else {
@@ -499,7 +499,7 @@ txMozillaXMLOutput::startElement(nsIAtom* aPrefix,
         nsId = kNameSpaceID_XHTML;
 
         nsAutoString lnameStr;
-        ToLowerCase(aLocalName, lnameStr);
+        TX_ToLowerCase(aLocalName, lnameStr);
         lname = do_GetAtom(lnameStr);
     }
     else {
@@ -802,7 +802,7 @@ txMozillaXMLOutput::endHTMLElement(nsIContent* aElement)
             nsAutoString value;
             aElement->GetAttr(kNameSpaceID_None, nsGkAtoms::content, value);
             if (!value.IsEmpty()) {
-                ToLowerCase(httpEquiv);
+                nsContentUtils::ASCIIToLower(httpEquiv);
                 nsCOMPtr<nsIAtom> header = do_GetAtom(httpEquiv);
                 processHTTPEquiv(header, value);
             }