--- a/mfbt/Compression.cpp
+++ b/mfbt/Compression.cpp
@@ -7,37 +7,20 @@
 #include "mozilla/Compression.h"
 #include "mozilla/CheckedInt.h"
 
 // Without including <string>, MSVC 2015 complains about e.g. the impossibility
 // to convert `const void* const` to `void*` when calling memchr from
 // corecrt_memory.h.
 #include <string>
 
-// Because we wrap lz4.c in an anonymous namespace, all of its #includes
-// go in the anonymous namespace too. This would create conflicting
-// declarations for intrinsic functions that are internally defined
-// at top-level. Including intrin.h here prevents it from being included
-// later within the anonymous namespace.
-#ifdef _MSC_VER
-#include <intrin.h>
-#endif
+#include "lz4.h"
 
 using namespace mozilla::Compression;
 
-namespace {
-
-extern "C" {
-
-#include "lz4.c"
-
-}
-
-}/* anonymous namespace */
-
 /* Our wrappers */
 
 size_t
 LZ4::compress(const char* aSource, size_t aInputSize, char* aDest)
 {
   CheckedInt<int> inputSizeChecked = aInputSize;
   MOZ_ASSERT(inputSizeChecked.isValid());
   return LZ4_compress_default(aSource, aDest, inputSizeChecked.value(),

--- a/mfbt/lz4.h
+++ b/mfbt/lz4.h
@@ -67,30 +67,34 @@ extern "C" {
 */
 
 /*^***************************************************************
 *  Export parameters
 *****************************************************************/
 /*
 *  LZ4_DLL_EXPORT :
 *  Enable exporting of functions when building a Windows DLL
-*  LZ4LIB_API :
+*  LZ4LIB_VISIBILITY :
 *  Control library symbols visibility.
 */
+#ifndef LZ4LIB_VISIBILITY
+#  if defined(__GNUC__) && (__GNUC__ >= 4)
+#    define LZ4LIB_VISIBILITY __attribute__ ((visibility ("default")))
+#  else
+#    define LZ4LIB_VISIBILITY
+#  endif
+#endif
 #if defined(LZ4_DLL_EXPORT) && (LZ4_DLL_EXPORT==1)
-#  define LZ4LIB_API __declspec(dllexport)
+#  define LZ4LIB_API __declspec(dllexport) LZ4LIB_VISIBILITY
 #elif defined(LZ4_DLL_IMPORT) && (LZ4_DLL_IMPORT==1)
-#  define LZ4LIB_API __declspec(dllimport) /* It isn't required but allows to generate better code, saving a function pointer load from the IAT and an indirect jump.*/
-#elif defined(__GNUC__) && (__GNUC__ >= 4)
-#  define LZ4LIB_API __attribute__ ((__visibility__ ("default")))
+#  define LZ4LIB_API __declspec(dllimport) LZ4LIB_VISIBILITY /* It isn't required but allows to generate better code, saving a function pointer load from the IAT and an indirect jump.*/
 #else
-#  define LZ4LIB_API
+#  define LZ4LIB_API LZ4LIB_VISIBILITY
 #endif
 
-
 /*------   Version   ------*/
 #define LZ4_VERSION_MAJOR    1    /* for breaking interface changes  */
 #define LZ4_VERSION_MINOR    8    /* for new (non-breaking) interface capabilities */
 #define LZ4_VERSION_RELEASE  0    /* for tweaks, bug-fixes, or development */
 
 #define LZ4_VERSION_NUMBER (LZ4_VERSION_MAJOR *100*100 + LZ4_VERSION_MINOR *100 + LZ4_VERSION_RELEASE)
 
 #define LZ4_LIB_VERSION LZ4_VERSION_MAJOR.LZ4_VERSION_MINOR.LZ4_VERSION_RELEASE

--- a/mfbt/moz.build
+++ b/mfbt/moz.build
@@ -142,29 +142,21 @@ UNIFIED_SOURCES += [
     'Unused.cpp',
 ]
 
 DEFINES['IMPL_MFBT'] = True
 
 SOURCES += [
     'Compression.cpp',
     'decimal/Decimal.cpp',
+    'lz4.c',
 ]
 
 DisableStlWrapping()
 
-# Suppress warnings in third-party LZ4 code.
-# TODO: Remove these suppressions after bug 993267 is fixed.
-
-if CONFIG['GNU_CXX']:
-    SOURCES['Compression.cpp'].flags += ['-Wno-unused-function']
-    CXXFLAGS += ['-Wno-error=shadow']
-
 if CONFIG['CLANG_CXX']:
     # Suppress warnings from third-party V8 Decimal code.
     SOURCES['decimal/Decimal.cpp'].flags += ['-Wno-implicit-fallthrough']
 
-if CONFIG['_MSC_VER']:
-    # Error 4804 is "'>' : unsafe use of type 'bool' in operation"
-    SOURCES['Compression.cpp'].flags += ['-wd4804']
-
 if CONFIG['MOZ_NEEDS_LIBATOMIC']:
     OS_LIBS += ['atomic']
+
+DEFINES['LZ4LIB_VISIBILITY'] = ''