--- a/layout/style/nsMediaFeatures.cpp
+++ b/layout/style/nsMediaFeatures.cpp
@@ -35,20 +35,20 @@ static const nsCSSProps::KTableEntry kOr
 
 static const nsCSSProps::KTableEntry kScanKeywords[] = {
   { eCSSKeyword_progressive,              NS_STYLE_SCAN_PROGRESSIVE },
   { eCSSKeyword_interlace,                NS_STYLE_SCAN_INTERLACE },
   { eCSSKeyword_UNKNOWN,                  -1 }
 };
 
 static const nsCSSProps::KTableEntry kDisplayModeKeywords[] = {
-  { eCSSKeyword_browser,                 NS_STYLE_DISPLAY_MODE_BROWSER },
-  { eCSSKeyword_minimal_ui,              NS_STYLE_DISPLAY_MODE_MINIMAL_UI },
-  { eCSSKeyword_standalone,              NS_STYLE_DISPLAY_MODE_STANDALONE },
-  { eCSSKeyword_fullscreen,              NS_STYLE_DISPLAY_MODE_FULLSCREEN },
+  { eCSSKeyword_browser,                 StyleDisplayMode::Browser, },
+  { eCSSKeyword_minimal_ui,              StyleDisplayMode::MinimalUI },
+  { eCSSKeyword_standalone,              StyleDisplayMode::Standalone },
+  { eCSSKeyword_fullscreen,              StyleDisplayMode::Fullscreen },
   { eCSSKeyword_UNKNOWN,                 -1 }
 };
 
 #ifdef XP_WIN
 struct WindowsThemeName {
   LookAndFeel::WindowsTheme id;
   const wchar_t* name;
 };
@@ -303,17 +303,17 @@ GetScan(nsPresContext* aPresContext, con
 static void
 GetDisplayMode(nsPresContext* aPresContext, const nsMediaFeature*,
                nsCSSValue& aResult)
 {
   nsCOMPtr<nsISupports> container;
   RefPtr<nsIDocShell> docShell;
 
   if (!aPresContext) {
-    aResult.SetIntValue(NS_STYLE_DISPLAY_MODE_BROWSER, eCSSUnit_Enumerated);
+    aResult.SetIntValue(static_cast<int32_t>(StyleDisplayMode::Browser), eCSSUnit_Enumerated);
     return;
   }
 
   if (aPresContext) {
     // Calling GetRootPresContext() can be slow, so make sure to call it
     // just once.
     nsRootPresContext* root = aPresContext->GetRootPresContext();
     if (root && root->Document()) {
@@ -324,28 +324,28 @@ GetDisplayMode(nsPresContext* aPresConte
 
   nsCOMPtr<nsIBaseWindow> baseWindow = do_QueryInterface(container);
   if (baseWindow) {
     nsCOMPtr<nsIWidget> mainWidget;
     baseWindow->GetMainWidget(getter_AddRefs(mainWidget));
     nsSizeMode mode = mainWidget ? mainWidget->SizeMode() : nsSizeMode_Normal;
 
     if (mode == nsSizeMode_Fullscreen) {
-      aResult.SetIntValue(NS_STYLE_DISPLAY_MODE_FULLSCREEN, eCSSUnit_Enumerated);
+      aResult.SetIntValue(static_cast<int32_t>(StyleDisplayMode::Fullscreen), eCSSUnit_Enumerated);
       return;
     }
   }
 
-  static_assert(nsIDocShell::DISPLAY_MODE_BROWSER == NS_STYLE_DISPLAY_MODE_BROWSER &&
-                nsIDocShell::DISPLAY_MODE_MINIMAL_UI == NS_STYLE_DISPLAY_MODE_MINIMAL_UI &&
-                nsIDocShell::DISPLAY_MODE_STANDALONE == NS_STYLE_DISPLAY_MODE_STANDALONE &&
-                nsIDocShell::DISPLAY_MODE_FULLSCREEN == NS_STYLE_DISPLAY_MODE_FULLSCREEN,
-                "nsIDocShell display modes must mach nsStyleConsts.h");
+  static_assert(nsIDocShell::DISPLAY_MODE_BROWSER == static_cast<uint32_t>(StyleDisplayMode::Browser)  &&
+                nsIDocShell::DISPLAY_MODE_MINIMAL_UI == static_cast<uint32_t>(StyleDisplayMode::MinimalUI) &&
+                nsIDocShell::DISPLAY_MODE_STANDALONE == static_cast<uint32_t>(StyleDisplayMode::Standalone) &&
+                nsIDocShell::DISPLAY_MODE_FULLSCREEN == static_cast<uint32_t>(StyleDisplayMode::Fullscreen),
+                "nsIDocShell display modes must match nsStyleConsts.h");
 
-  uint32_t displayMode = NS_STYLE_DISPLAY_MODE_BROWSER;
+  uint32_t displayMode = static_cast<uint32_t>(StyleDisplayMode::Browser);
   if (docShell) {
     docShell->GetDisplayMode(&displayMode);
   }
 
   aResult.SetIntValue(displayMode, eCSSUnit_Enumerated);
 }
 
 static void

--- a/layout/style/nsStyleConsts.h
+++ b/layout/style/nsStyleConsts.h
@@ -1199,16 +1199,18 @@ enum class StyleWhiteSpace : uint8_t {
 #define NS_STYLE_ORIENTATION_PORTRAIT           0
 #define NS_STYLE_ORIENTATION_LANDSCAPE          1
 
 // scan
 #define NS_STYLE_SCAN_PROGRESSIVE               0
 #define NS_STYLE_SCAN_INTERLACE                 1
 
 // display-mode
-#define NS_STYLE_DISPLAY_MODE_BROWSER           0
-#define NS_STYLE_DISPLAY_MODE_MINIMAL_UI        1
-#define NS_STYLE_DISPLAY_MODE_STANDALONE        2
-#define NS_STYLE_DISPLAY_MODE_FULLSCREEN        3
+enum class StyleDisplayMode : uint8_t {
+	Browser,
+	MinimalUI,
+	Standalone,
+	Fullscreen,
+};
 
 } // namespace mozilla
 
 #endif /* nsStyleConsts_h___ */