--- a/dom/media/gmp/ChromiumCDMAdapter.cpp
+++ b/dom/media/gmp/ChromiumCDMAdapter.cpp
@@ -10,17 +10,17 @@
 #include "gmp-api/gmp-entrypoints.h"
 #include "gmp-api/gmp-decryption.h"
 #include "gmp-api/gmp-video-codec.h"
 #include "gmp-api/gmp-platform.h"
 #include "WidevineUtils.h"
 #include "GMPLog.h"
 #include "mozilla/Move.h"
 
-#if defined(XP_MACOSX) || defined(XP_LINUX)
+#ifndef XP_WIN
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <unistd.h>
 #include <fcntl.h>
 #endif
 
 // Declared in WidevineAdapter.cpp.
 extern const GMPPlatformAPI* sPlatform;
@@ -193,17 +193,17 @@ HostFile::HostFile(const nsCString& aPat
                               NULL,
                               OPEN_EXISTING,
                               0,
                               NULL);
   mFile = (handle == INVALID_HANDLE_VALUE) ? cdm::kInvalidPlatformFile : handle;
 }
 #endif
 
-#if defined(XP_MACOSX) || defined(XP_LINUX)
+#ifndef XP_WIN
 HostFile::HostFile(const nsCString& aPath)
   : mPath(aPath)
 {
   // Note: open() returns -1 on failure; i.e. kInvalidPlatformFile.
   mFile = open(aPath.get(), O_RDONLY);
 }
 #endif
 

--- a/dom/media/gmp/ChromiumCDMAdapter.h
+++ b/dom/media/gmp/ChromiumCDMAdapter.h
@@ -12,17 +12,17 @@
 #include "nsTArray.h"
 #include "content_decryption_module_ext.h"
 #include "nsString.h"
 
 struct GMPPlatformAPI;
 
 namespace mozilla {
 
-#if defined(OS_WIN)
+#if defined(XP_WIN)
 typedef nsString HostFileString;
 #else
 typedef nsCString HostFileString;
 #endif
 
 class HostFile
 {
 public:

--- a/dom/media/gmp/GMPChild.cpp
+++ b/dom/media/gmp/GMPChild.cpp
@@ -340,25 +340,25 @@ GMPChild::GetUTF8LibPath(nsACString& aOu
   nsAutoString path;
   libFile->GetPath(path);
   aOutLibPath = NS_ConvertUTF16toUTF8(path);
 
   return true;
 #endif
 }
 
-#if defined(XP_MACOSX)
+#if defined(XP_WIN)
+#define FIREFOX_FILE NS_LITERAL_STRING("firefox.exe")
+#define XUL_LIB_FILE NS_LITERAL_STRING("xul.dll")
+#elif defined(XP_MACOSX)
 #define FIREFOX_FILE NS_LITERAL_STRING("firefox")
 #define XUL_LIB_FILE NS_LITERAL_STRING("XUL")
-#elif defined(XP_LINUX)
+#else
 #define FIREFOX_FILE NS_LITERAL_STRING("firefox")
 #define XUL_LIB_FILE NS_LITERAL_STRING("libxul.so")
-#elif defined(OS_WIN)
-#define FIREFOX_FILE NS_LITERAL_STRING("firefox.exe")
-#define XUL_LIB_FILE NS_LITERAL_STRING("xul.dll")
 #endif
 
 #if defined(XP_MACOSX)
 static bool
 GetFirefoxAppPath(nsCOMPtr<nsIFile> aPluginContainerPath,
                   nsCOMPtr<nsIFile>& aOutFirefoxAppPath)
 {
   // aPluginContainerPath will end with something like:
@@ -407,29 +407,29 @@ GMPChild::MakeCDMHostVerificationPaths()
   } else {
     // Without successfully determining plugin-container's path, we can't
     // determine libxul's or Firefox's. So give up.
     return paths;
   }
 
   // Firefox application binary path.
   nsCOMPtr<nsIFile> appDir;
-#if defined(XP_WIN) || defined(XP_LINUX)
-  // Note: re-using 'path' var here, as on Windows/Linux we assume Firefox
-  // executable is in the same directory as plugin-container.
-  if (NS_SUCCEEDED(path->GetParent(getter_AddRefs(appDir))) &&
+#if defined(XP_MACOSX)
+  // On MacOS the firefox binary is a few parent directories up from
+  // plugin-container.
+  if (GetFirefoxAppPath(path, appDir) &&
       NS_SUCCEEDED(appDir->Clone(getter_AddRefs(path))) &&
       NS_SUCCEEDED(path->Append(FIREFOX_FILE)) && FileExists(path) &&
       ResolveLinks(path) && NS_SUCCEEDED(path->GetPath(str))) {
     paths.AppendElement(NS_ConvertUTF16toUTF8(str));
   }
-#elif defined(XP_MACOSX)
-  // On MacOS the firefox binary is a few parent directories up from
-  // plugin-container.
-  if (GetFirefoxAppPath(path, appDir) &&
+#else
+  // Note: re-using 'path' var here, as on Windows/Linux we assume Firefox
+  // executable is in the same directory as plugin-container.
+  if (NS_SUCCEEDED(path->GetParent(getter_AddRefs(appDir))) &&
       NS_SUCCEEDED(appDir->Clone(getter_AddRefs(path))) &&
       NS_SUCCEEDED(path->Append(FIREFOX_FILE)) && FileExists(path) &&
       ResolveLinks(path) && NS_SUCCEEDED(path->GetPath(str))) {
     paths.AppendElement(NS_ConvertUTF16toUTF8(str));
   }
 #endif
   // Libxul path. Note: re-using 'path' var here, as we assume libxul is in
   // the same directory as Firefox executable.

--- a/media/gmp-clearkey/0.1/gmp-clearkey.cpp
+++ b/media/gmp-clearkey/0.1/gmp-clearkey.cpp
@@ -22,17 +22,17 @@
 #include "ClearKeyCDM.h"
 #include "ClearKeySessionManager.h"
 // This include is required in order for content_decryption_module to work
 // on Unix systems.
 #include "stddef.h"
 #include "content_decryption_module.h"
 #include "content_decryption_module_ext.h"
 
-#if defined(XP_MACOSX) || defined(XP_LINUX)
+#ifndef XP_WIN
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <unistd.h>
 #endif
 
 #ifdef ENABLE_WMF
 #include "WMFUtils.h"
 #endif // ENABLE_WMF
@@ -83,29 +83,27 @@ bool
 CanReadSome(cdm::PlatformFile aFile)
 {
   vector<uint8_t> data;
   data.resize(TEST_READ_SIZE);
 #ifdef XP_WIN
   DWORD bytesRead = 0;
   return ReadFile(aFile, &data.front(), TEST_READ_SIZE, &bytesRead, nullptr) &&
          bytesRead > 0;
-#elif defined(XP_MACOSX) || defined(XP_LINUX)
+#else
   return read(aFile, &data.front(), TEST_READ_SIZE) > 0;
-#else
-  return false;
 #endif
 }
 
 void
 ClosePlatformFile(cdm::PlatformFile aFile)
 {
 #ifdef XP_WIN
   CloseHandle(aFile);
-#elif defined(XP_MACOSX) || defined(XP_LINUX)
+#else
   close(aFile);
 #endif
 }
 
 CDM_API
 bool
 VerifyCdmHost_0(const cdm::HostFile* aHostFiles, uint32_t aNumFiles)
 {