diff --git a/layout/style/CSSNestingLowerer.cpp b/layout/style/CSSNestingFlattener.cpp
similarity index 98%
rename from layout/style/CSSNestingLowerer.cpp
rename to layout/style/CSSNestingFlattener.cpp
index 2dd45d58a9..ac8fc1a2ca 100644
--- a/layout/style/CSSNestingLowerer.cpp
+++ b/layout/style/CSSNestingFlattener.cpp
@@ -3,7 +3,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-#include "CSSNestingLowerer.h"
+#include "CSSNestingFlattener.h"
 
 #include "mozilla/Assertions.h"
 #include "nsString.h"
@@ -14,22 +14,22 @@ namespace css {
 
 namespace {
 
-class CSSNestingLowerer final
+class CSSNestingFlattener final
 {
   using SelectorList = nsTArray<nsString>;
 
 public:
-  explicit CSSNestingLowerer(const nsAString& aInput)
+  explicit CSSNestingFlattener(const nsAString& aInput)
     : mInput(aInput)
     , mPos(0)
     , mSawNesting(false)
   {
   }
 
-  bool Lower(nsAString& aOutput)
+  bool Flatten(nsAString& aOutput)
   {
-    nsAutoString lowered;
-    if (!ProcessStylesheet(lowered, false)) {
+    nsAutoString flattened;
+    if (!ProcessStylesheet(flattened, false)) {
       return false;
     }
 
@@ -38,7 +38,7 @@ public:
       return false;
     }
 
-    aOutput.Assign(lowered);
+    aOutput.Assign(flattened);
     return true;
   }
 
@@ -952,10 +952,10 @@ private:
 } // namespace
 
 bool
-LowerBasicCSSNesting(const nsAString& aInput, nsAString& aOutput)
+FlattenBasicCSSNesting(const nsAString& aInput, nsAString& aOutput)
 {
-  CSSNestingLowerer lowerer(aInput);
-  return lowerer.Lower(aOutput);
+  CSSNestingFlattener flattener(aInput);
+  return flattener.Flatten(aOutput);
 }
 
 } // namespace css
diff --git a/layout/style/CSSNestingLowerer.h b/layout/style/CSSNestingFlattener.h
similarity index 69%
rename from layout/style/CSSNestingLowerer.h
rename to layout/style/CSSNestingFlattener.h
index b74645186f..41a9d4432d 100644
--- a/layout/style/CSSNestingLowerer.h
+++ b/layout/style/CSSNestingFlattener.h
@@ -3,17 +3,17 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-#ifndef CSSNestingLowerer_h
-#define CSSNestingLowerer_h
+#ifndef CSSNestingFlattener_h
+#define CSSNestingFlattener_h
 
 class nsAString;
 
 namespace mozilla {
 namespace css {
 
-bool LowerBasicCSSNesting(const nsAString& aInput, nsAString& aOutput);
+bool FlattenBasicCSSNesting(const nsAString& aInput, nsAString& aOutput);
 
 } // namespace css
 } // namespace mozilla
 
-#endif // CSSNestingLowerer_h
+#endif // CSSNestingFlattener_h
diff --git a/layout/style/moz.build b/layout/style/moz.build
index e10c834daa..3dfbd58012 100644
--- a/layout/style/moz.build
+++ b/layout/style/moz.build
@@ -127,7 +127,7 @@ UNIFIED_SOURCES += [
     'CounterStyleManager.cpp',
     'CSS.cpp',
     'CSSLexer.cpp',
-    'CSSNestingLowerer.cpp',
+    'CSSNestingFlattener.cpp',
     'CSSRuleList.cpp',
     'CSSStyleSheet.cpp',
     'CSSVariableDeclarations.cpp',
diff --git a/layout/style/nsCSSParser.cpp b/layout/style/nsCSSParser.cpp
index 6ca421a09b..6e24a427b0 100644
--- a/layout/style/nsCSSParser.cpp
+++ b/layout/style/nsCSSParser.cpp
@@ -18,7 +18,7 @@
 #include <regex>     // for std::regex and std::regex_match
 
 #include "nsCSSParser.h"
-#include "CSSNestingLowerer.h"
+#include "CSSNestingFlattener.h"
 #include "nsAlgorithm.h"
 #include "nsCSSProps.h"
 #include "nsCSSKeywords.h"
@@ -1826,11 +1826,11 @@ CSSParserImpl::ParseSheet(const nsAString& aInput,
                "Sheet principal does not match passed principal");
 #endif
 
-  nsAutoString loweredInput;
+  nsAutoString flattenedInput;
   const nsAString* input = &aInput;
   if (sNestingEnabled &&
-      mozilla::css::LowerBasicCSSNesting(aInput, loweredInput)) {
-    input = &loweredInput;
+      mozilla::css::FlattenBasicCSSNesting(aInput, flattenedInput)) {
+    input = &flattenedInput;
   }
 
   nsCSSScanner scanner(*input, aLineNumber);