--- a/widget/windows/KeyboardLayout.cpp
+++ b/widget/windows/KeyboardLayout.cpp
@@ -267,17 +267,17 @@ GetKeyLocationName(uint32_t aLocation)
 }
 
 static const nsCString
 GetCharacterCodeName(const char16_t* aChars, uint32_t aLength)
 {
   if (!aLength) {
     return EmptyCString();
   }
-  nsAutoCString result;
+  nsCString result;
   for (uint32_t i = 0; i < aLength; ++i) {
     if (!result.IsEmpty()) {
       result.AppendLiteral(", ");
     } else {
       result.AssignLiteral("\"");
     }
     result.Append(GetCharacterCodeName(aChars[i]));
   }
@@ -286,17 +286,17 @@ GetCharacterCodeName(const char16_t* aCh
 }
 
 static const nsCString
 GetCharacterCodeName(const UniCharsAndModifiers& aUniCharsAndModifiers)
 {
   if (aUniCharsAndModifiers.IsEmpty()) {
     return EmptyCString();
   }
-  nsAutoCString result;
+  nsCString result;
   for (uint32_t i = 0; i < aUniCharsAndModifiers.Length(); i++) {
     if (!result.IsEmpty()) {
       result.AppendLiteral(", ");
     } else {
       result.AssignLiteral("\"");
     }
     result.Append(GetCharacterCodeName(aUniCharsAndModifiers.CharAt(i)));
   }
@@ -573,17 +573,17 @@ private:
       AppendLiteral(" | ");
     }
   }
 };
 
 static const nsCString
 ToString(const MSG& aMSG)
 {
-  nsAutoCString result;
+  nsCString result;
   result.AssignLiteral("{ message=");
   result.Append(GetMessageName(aMSG.message).get());
   result.AppendLiteral(", ");
   switch (aMSG.message) {
     case WM_KEYDOWN:
     case WM_KEYUP:
     case WM_SYSKEYDOWN:
     case WM_SYSKEYUP:
@@ -636,17 +636,17 @@ ToString(const MSG& aMSG)
 }
 
 static const nsCString
 ToString(const UniCharsAndModifiers& aUniCharsAndModifiers)
 {
   if (aUniCharsAndModifiers.IsEmpty()) {
     return NS_LITERAL_CSTRING("{}");
   }
-  nsAutoCString result;
+  nsCString result;
   result.AssignLiteral("{ ");
   result.Append(GetCharacterCodeName(aUniCharsAndModifiers.CharAt(0)));
   for (size_t i = 1; i < aUniCharsAndModifiers.Length(); ++i) {
     if (aUniCharsAndModifiers.ModifiersAt(i - 1) !=
           aUniCharsAndModifiers.ModifiersAt(i)) {
       result.AppendLiteral(" [");
       result.Append(GetModifiersName(aUniCharsAndModifiers.ModifiersAt(0)));
       result.AppendLiteral("]");
@@ -659,17 +659,17 @@ ToString(const UniCharsAndModifiers& aUn
   result.Append(GetModifiersName(aUniCharsAndModifiers.ModifiersAt(lastIndex)));
   result.AppendLiteral("] }");
   return result;
 }
 
 const nsCString
 ToString(const ModifierKeyState& aModifierKeyState)
 {
-  nsAutoCString result;
+  nsCString result;
   result.AssignLiteral("{ ");
   result.Append(GetModifiersName(aModifierKeyState.GetModifiers()).get());
   result.AppendLiteral(" }");
   return result;
 }
 
 // Unique id counter associated with a keydown / keypress events. Used in
 // identifing keypress events for removal from async event dispatch queue
@@ -2852,17 +2852,17 @@ NativeKey::NeedsToHandleWithoutFollowing
 
 static nsCString
 GetResultOfInSendMessageEx()
 {
   DWORD ret = ::InSendMessageEx(nullptr);
   if (!ret) {
     return NS_LITERAL_CSTRING("ISMEX_NOSEND");
   }
-  nsAutoCString result;
+  nsCString result;
   if (ret & ISMEX_CALLBACK) {
     result = "ISMEX_CALLBACK";
   }
   if (ret & ISMEX_NOTIFY) {
     if (!result.IsEmpty()) {
       result += " | ";
     }
     result += "ISMEX_NOTIFY";
@@ -4192,17 +4192,17 @@ KeyboardLayout::GetLayoutName(HKL aLayou
                                              key.get(), L"Layout Text",
                                              buf, sizeof(buf)))) {
       return NS_LITERAL_CSTRING("No name or too long name");
     }
     return NS_ConvertUTF16toUTF8(buf);
   }
 
   if (NS_WARN_IF((layout & 0xF000) != 0xF000)) {
-    nsAutoCString result;
+    nsCString result;
     result.AppendPrintf("Odd HKL: 0x%08X",
                         reinterpret_cast<uintptr_t>(aLayout));
     return result;
   }
 
   // Otherwise, we need to walk the registry under "Keyboard Layouts".
   nsCOMPtr<nsIWindowsRegKey> regKey =
     do_CreateInstance("@mozilla.org/windows-registry-key;1");

--- a/widget/windows/TSFTextStore.cpp
+++ b/widget/windows/TSFTextStore.cpp
@@ -63,17 +63,17 @@ HandleSeparator(nsCString& aDesc)
   if (!aDesc.IsEmpty()) {
     aDesc.AppendLiteral(" | ");
   }
 }
 
 static const nsCString
 GetFindFlagName(DWORD aFindFlag)
 {
-  nsAutoCString description;
+  nsCString description;
   if (!aFindFlag) {
     description.AppendLiteral("no flags (0)");
     return description;
   }
   if (aFindFlag & TS_ATTR_FIND_BACKWARDS) {
     description.AppendLiteral("TS_ATTR_FIND_BACKWARDS");
   }
   if (aFindFlag & TS_ATTR_FIND_WANT_OFFSET) {
@@ -157,17 +157,17 @@ static nsCString
 GetCLSIDNameStr(REFCLSID aCLSID)
 {
   LPOLESTR str = nullptr;
   HRESULT hr = ::StringFromCLSID(aCLSID, &str);
   if (FAILED(hr) || !str || !str[0]) {
     return EmptyCString();
   }
 
-  nsAutoCString result;
+  nsCString result;
   result = NS_ConvertUTF16toUTF8(str);
   ::CoTaskMemFree(str);
   return result;
 }
 
 static nsCString
 GetGUIDNameStr(REFGUID aGUID)
 {
@@ -286,17 +286,17 @@ GetRIIDNameStr(REFIID aRIID)
   HRESULT hr = ::StringFromIID(aRIID, &str);
   if (FAILED(hr) || !str || !str[0]) {
     return EmptyCString();
   }
 
   nsAutoString key(L"Interface\\");
   key += str;
 
-  nsAutoCString result;
+  nsCString result;
   wchar_t buf[256];
   if (WinUtils::GetRegistryKey(HKEY_CLASSES_ROOT, key.get(), nullptr,
                                buf, sizeof(buf))) {
     result = NS_ConvertUTF16toUTF8(buf);
   } else {
     result = NS_ConvertUTF16toUTF8(str);
   }
 
@@ -366,17 +366,17 @@ GetTextStoreReturnValueName(HRESULT aRes
     default:
       return GetCommonReturnValueName(aResult);
   }
 }
 
 static const nsCString
 GetSinkMaskNameStr(DWORD aSinkMask)
 {
-  nsAutoCString description;
+  nsCString description;
   if (aSinkMask & TS_AS_TEXT_CHANGE) {
     description.AppendLiteral("TS_AS_TEXT_CHANGE");
   }
   if (aSinkMask & TS_AS_SEL_CHANGE) {
     HandleSeparator(description);
     description.AppendLiteral("TS_AS_SEL_CHANGE");
   }
   if (aSinkMask & TS_AS_LAYOUT_CHANGE) {
@@ -403,17 +403,17 @@ GetActiveSelEndName(TsActiveSelEnd aSelE
   return aSelEnd == TS_AE_NONE  ? "TS_AE_NONE" :
          aSelEnd == TS_AE_START ? "TS_AE_START" :
          aSelEnd == TS_AE_END   ? "TS_AE_END" : "Unknown";
 }
 
 static const nsCString
 GetLockFlagNameStr(DWORD aLockFlags)
 {
-  nsAutoCString description;
+  nsCString description;
   if ((aLockFlags & TS_LF_READWRITE) == TS_LF_READWRITE) {
     description.AppendLiteral("TS_LF_READWRITE");
   } else if (aLockFlags & TS_LF_READ) {
     description.AppendLiteral("TS_LF_READ");
   }
   if (aLockFlags & TS_LF_SYNC) {
     if (!description.IsEmpty()) {
       description.AppendLiteral(" | ");
@@ -502,17 +502,17 @@ GetClauseAttrName(TF_DA_ATTR_INFO aAttr)
       return nsPrintfCString("Unknown(%08X)", static_cast<int32_t>(aAttr));
     }
   }
 }
 
 static nsCString
 GetDisplayAttrStr(const TF_DISPLAYATTRIBUTE& aDispAttr)
 {
-  nsAutoCString str;
+  nsCString str;
   str = "crText:{ ";
   str += GetColorName(aDispAttr.crText);
   str += " }, crBk:{ ";
   str += GetColorName(aDispAttr.crBk);
   str += " }, lsStyle: ";
   str += GetLineStyleName(aDispAttr.lsStyle);
   str += ", fBoldLine: ";
   str += GetBoolName(aDispAttr.fBoldLine);
@@ -544,17 +544,17 @@ GetMouseButtonName(int16_t aButton)
   }
 
 static nsCString
 GetMouseButtonsName(int16_t aButtons)
 {
   if (!aButtons) {
     return NS_LITERAL_CSTRING("no buttons");
   }
-  nsAutoCString names;
+  nsCString names;
   if (aButtons & WidgetMouseEventBase::eLeftButtonFlag) {
     names = "LeftButton";
   }
   if (aButtons & WidgetMouseEventBase::eRightButtonFlag) {
     ADD_SEPARATOR_IF_NECESSARY(names);
     names += "RightButton";
   }
   if (aButtons & WidgetMouseEventBase::eMiddleButtonFlag) {
@@ -573,17 +573,17 @@ GetMouseButtonsName(int16_t aButtons)
 }
 
 static nsCString
 GetModifiersName(Modifiers aModifiers)
 {
   if (aModifiers == MODIFIER_NONE) {
     return NS_LITERAL_CSTRING("no modifiers");
   }
-  nsAutoCString names;
+  nsCString names;
   if (aModifiers & MODIFIER_ALT) {
     names = NS_DOM_KEYNAME_ALT;
   }
   if (aModifiers & MODIFIER_ALTGRAPH) {
     ADD_SEPARATOR_IF_NECESSARY(names);
     names += NS_DOM_KEYNAME_ALTGRAPH;
   }
   if (aModifiers & MODIFIER_CAPSLOCK) {