--- a/memory/mozalloc/mozalloc.cpp
+++ b/memory/mozalloc/mozalloc.cpp
@@ -2,23 +2,17 @@
  * vim: sw=4 ts=4 et :
  */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * 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 <stddef.h>             // for size_t
 
-// Building with USE_STATIC_LIBS = True sets -MT instead of -MD. -MT sets _MT,
-// while -MD sets _MT and _DLL.
-#if defined(_MT) && !defined(_DLL)
-#define MOZ_STATIC_RUNTIME
-#endif
-
-#if defined(MOZ_MEMORY) && !defined(MOZ_STATIC_RUNTIME)
+#if defined(MOZ_MEMORY)
 // mozalloc.cpp is part of the same library as mozmemory, thus MOZ_MEMORY_IMPL
 // is needed.
 #define MOZ_MEMORY_IMPL
 #include "mozmemory_wrap.h"
 
 #if defined(XP_DARWIN)
 #include <malloc/malloc.h> // for malloc_size
 #endif
@@ -192,17 +186,16 @@ moz_xvalloc(size_t size)
     if (UNLIKELY(!ptr)) {
         mozalloc_handle_oom(size);
         return moz_xvalloc(size);
     }
     return ptr;
 }
 #endif // if defined(HAVE_VALLOC)
 
-#ifndef MOZ_STATIC_RUNTIME
 size_t
 moz_malloc_usable_size(void *ptr)
 {
     if (!ptr)
         return 0;
 
 #if defined(XP_DARWIN)
     return malloc_size(ptr);
@@ -236,9 +229,8 @@ moz_malloc_enclosing_size_of(const void 
 #if defined(MOZ_MEMORY)
     jemalloc_ptr_info_t info;
     jemalloc_ptr_info(ptr, &info);
     return jemalloc_ptr_is_live(&info) ? info.size : 0;
 #else
     return 0;
 #endif
 }
-#endif

--- a/memory/mozalloc/winheap.cpp
+++ b/memory/mozalloc/winheap.cpp
@@ -3,23 +3,17 @@
  */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * 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 "mozilla/Types.h"
 #include <windows.h>
 
-// Building with USE_STATIC_LIBS = True sets -MT instead of -MD. -MT sets _MT,
-// while -MD sets _MT and _DLL.
-#if defined(_MT) && !defined(_DLL)
-#define MOZ_STATIC_RUNTIME
-#endif
-
-#if defined(MOZ_MEMORY) && !defined(MOZ_STATIC_RUNTIME)
+#if defined(MOZ_MEMORY)
 // mozalloc.cpp is part of the same library as mozmemory, thus MOZ_MEMORY_IMPL
 // is needed.
 #define MOZ_MEMORY_IMPL
 #include "mozmemory_wrap.h"
 
 // See mozmemory_wrap.h for more details. This file is part of libmozglue, so
 // it needs to use _impl suffixes. However, with libmozglue growing, this is
 // becoming cumbersome, so we will likely use a malloc.h wrapper of some sort