diff --git a/b2g/installer/Makefile.in b/b2g/installer/Makefile.in
index 80c8059ec6d1..6ff3769023a3 100644
--- a/b2g/installer/Makefile.in
+++ b/b2g/installer/Makefile.in
@@ -83,9 +83,6 @@ ifdef GKMEDIAS_SHARED_LIBRARY
 DEFINES += -DGKMEDIAS_SHARED_LIBRARY
 endif
 
-ifdef MOZ_REPLACE_MALLOC
-DEFINES += -DMOZ_REPLACE_MALLOC
-endif
 ifdef MOZ_JEMALLOC3
 DEFINES += -DMOZ_JEMALLOC3
 endif
diff --git a/browser/installer/Makefile.in b/browser/installer/Makefile.in
index 560bae36d560..34995e594026 100644
--- a/browser/installer/Makefile.in
+++ b/browser/installer/Makefile.in
@@ -137,9 +137,6 @@ endif
 ifdef MOZ_SHARED_ICU
 DEFINES += -DMOZ_SHARED_ICU
 endif
-ifdef MOZ_REPLACE_MALLOC
-DEFINES += -DMOZ_REPLACE_MALLOC
-endif
 ifdef MOZ_JEMALLOC3
 DEFINES += -DMOZ_JEMALLOC3
 endif
diff --git a/configure.in b/configure.in
index 809ddbf7062f..411d4f3f7611 100644
--- a/configure.in
+++ b/configure.in
@@ -7161,6 +7161,7 @@ if test -n "$MOZ_REPLACE_MALLOC" -a -z "$MOZ_MEMORY"; then
     dnl deliberate choice not to enable it (bug 702250, for instance)
     AC_MSG_ERROR([--enable-replace-malloc requires --enable-jemalloc])
 elif test -n "$MOZ_REPLACE_MALLOC"; then
+    AC_DEFINE(MOZ_REPLACE_MALLOC)
     MOZ_NATIVE_JEMALLOC=
 
     dnl Replace-malloc Mac linkage quirks
diff --git a/memory/build/malloc_decls.h b/memory/build/malloc_decls.h
index e46cf593b876..a1a1d70508e3 100644
--- a/memory/build/malloc_decls.h
+++ b/memory/build/malloc_decls.h
@@ -24,7 +24,9 @@ typedef const void * usable_ptr_t;
 #  define MALLOC_FUNCS_MALLOC 1
 #  define MALLOC_FUNCS_JEMALLOC 2
 #  define MALLOC_FUNCS_INIT 4
-#  define MALLOC_FUNCS_ALL (MALLOC_FUNCS_INIT | MALLOC_FUNCS_MALLOC | MALLOC_FUNCS_JEMALLOC)
+#  define MALLOC_FUNCS_BRIDGE 8
+#  define MALLOC_FUNCS_ALL (MALLOC_FUNCS_INIT | MALLOC_FUNCS_BRIDGE | \
+                            MALLOC_FUNCS_MALLOC | MALLOC_FUNCS_JEMALLOC)
 
 #endif /* malloc_decls_h */
 
@@ -36,6 +38,9 @@ typedef const void * usable_ptr_t;
 #  if MALLOC_FUNCS & MALLOC_FUNCS_INIT
 MALLOC_DECL(init, void, const malloc_table_t *)
 #  endif
+#  if MALLOC_FUNCS & MALLOC_FUNCS_BRIDGE
+MALLOC_DECL(get_bridge, struct ReplaceMallocBridge*, void)
+#  endif
 #  if MALLOC_FUNCS & MALLOC_FUNCS_MALLOC
 MALLOC_DECL(malloc, void *, size_t)
 MALLOC_DECL(posix_memalign, int, void **, size_t, size_t)
diff --git a/memory/build/moz.build b/memory/build/moz.build
index f66d234bd9c6..e6cf45a0a570 100644
--- a/memory/build/moz.build
+++ b/memory/build/moz.build
@@ -15,8 +15,8 @@ if CONFIG['MOZ_REPLACE_MALLOC']:
     EXPORTS += [
         'malloc_decls.h',
         'replace_malloc.h',
+        'replace_malloc_bridge.h',
     ]
-    DEFINES['MOZ_REPLACE_MALLOC'] = True
 
 SOURCES += [
     'jemalloc_config.c',
diff --git a/memory/build/replace_malloc.c b/memory/build/replace_malloc.c
index b7bbd85fdbca..06bf26b9bf2a 100644
--- a/memory/build/replace_malloc.c
+++ b/memory/build/replace_malloc.c
@@ -22,6 +22,7 @@
 #include "malloc_decls.h"
 
 #include "mozilla/Likely.h"
+
 /*
  * Windows doesn't come with weak imports as they are possible with
  * LD_PRELOAD or DYLD_INSERT_LIBRARIES on Linux/OSX. On this platform,
@@ -131,6 +132,16 @@ init()
     replace_init(&malloc_table);
 }
 
+MFBT_API struct ReplaceMallocBridge*
+get_bridge(void)
+{
+  if (MOZ_UNLIKELY(!replace_malloc_initialized))
+    init();
+  if (MOZ_LIKELY(!replace_get_bridge))
+    return NULL;
+  return replace_get_bridge();
+}
+
 void*
 malloc_impl(size_t size)
 {
diff --git a/memory/build/replace_malloc.h b/memory/build/replace_malloc.h
index 0cbec17ea3f5..c3a5737407c5 100644
--- a/memory/build/replace_malloc.h
+++ b/memory/build/replace_malloc.h
@@ -58,6 +58,15 @@
  * are taken care of by memory/replace/defs.mk.
  */
 
+#ifdef replace_malloc_bridge_h
+#error Do not include replace_malloc_bridge.h before replace_malloc.h. \
+  In fact, you only need the latter.
+#endif
+
+#define REPLACE_MALLOC_IMPL
+
+#include "replace_malloc_bridge.h"
+
 /* Implementing a replace-malloc library is incompatible with using mozalloc. */
 #define MOZ_NO_MOZALLOC 1
 
diff --git a/memory/build/replace_malloc_bridge.h b/memory/build/replace_malloc_bridge.h
new file mode 100644
index 000000000000..5deddaa71f28
--- /dev/null
+++ b/memory/build/replace_malloc_bridge.h
@@ -0,0 +1,93 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+#ifndef replace_malloc_bridge_h
+#define replace_malloc_bridge_h
+
+/*
+ * The replace-malloc bridge allows bidirectional method calls between
+ * a program and the replace-malloc library that has been loaded for it.
+ * In Firefox, this is used to allow method calls between code in libxul
+ * and code in the replace-malloc library, without libxul needing to link
+ * against that library or vice-versa.
+ *
+ * Subsystems can add methods for their own need. Replace-malloc libraries
+ * can decide to implement those methods or not.
+ *
+ * Replace-malloc libraries can provide such a bridge by implementing
+ * a ReplaceMallocBridge-derived class, and a replace_get_bridge function
+ * returning an instance of that class. The default methods in
+ * ReplaceMallocBridge are expected to return values that callers would
+ * understand as "the bridge doesn't implement this method", so that a
+ * replace-malloc library doesn't have to implement all methods.
+ *
+ * The ReplaceMallocBridge class contains definitions for methods for
+ * all replace-malloc libraries. Each library picks the methods it wants
+ * to reply to in its ReplaceMallocBridge-derived class instance.
+ * All methods of ReplaceMallocBridge must be virtual. Similarly,
+ * anything passed as an argument to those methods must be plain data, or
+ * an instance of a class with only virtual methods.
+ *
+ * Binary compatibility is expected to be maintained, such that a newer
+ * Firefox can be used with an old replace-malloc library, or an old
+ * Firefox can be used with a newer replace-malloc library. As such, only
+ * new virtual methods should be added to ReplaceMallocBridge, and
+ * each change should have a corresponding bump of the mVersion value.
+ * At the same time, each virtual method should have a corresponding
+ * wrapper calling the virtual method on the instance from
+ * ReplaceMallocBridge::Get(), giving it the version the virtual method
+ * was added.
+ *
+ * Parts that are not relevant to the replace-malloc library end of the
+ * bridge are hidden when REPLACE_MALLOC_IMPL is not defined, which is
+ * the case when including replace_malloc.h.
+ */
+
+struct ReplaceMallocBridge;
+
+#ifdef __cplusplus
+
+#include "mozilla/NullPtr.h"
+#include "mozilla/Types.h"
+
+#ifndef REPLACE_MALLOC_IMPL
+/* Returns the replace-malloc bridge if there is one to be returned. */
+extern "C" MFBT_API ReplaceMallocBridge* get_bridge();
+#endif
+
+struct ReplaceMallocBridge
+{
+  ReplaceMallocBridge() : mVersion(0) {}
+
+#ifndef REPLACE_MALLOC_IMPL
+  /* Returns the replace-malloc bridge if its version is at least the
+   * requested one. */
+  static ReplaceMallocBridge* Get(int aMinimumVersion) {
+    static ReplaceMallocBridge* sSingleton = get_bridge();
+    return (sSingleton && sSingleton->mVersion >= aMinimumVersion)
+      ? sSingleton : nullptr;
+  }
+#endif
+
+protected:
+  const int mVersion;
+};
+
+#ifndef REPLACE_MALLOC_IMPL
+/* Class containing wrappers for calls to ReplaceMallocBridge methods.
+ * Those wrappers need to be static methods in a class because compilers
+ * complain about unused static global functions, and linkers complain
+ * about multiple definitions of non-static global functions.
+ * Using a separate class from ReplaceMallocBridge allows the function
+ * names to be identical. */
+struct ReplaceMalloc
+{
+};
+#endif
+
+#endif /* __cplusplus */
+
+#endif /* replace_malloc_bridge_h */
diff --git a/memory/mozjemalloc/moz.build b/memory/mozjemalloc/moz.build
index f887ae1903ac..b912bc95f1b2 100644
--- a/memory/mozjemalloc/moz.build
+++ b/memory/mozjemalloc/moz.build
@@ -23,9 +23,6 @@ if CONFIG['MOZ_UPDATE_CHANNEL'] not in ('release', 'esr'):
 
 DEFINES['abort'] = 'moz_abort'
 
-if CONFIG['MOZ_REPLACE_MALLOC']:
-    DEFINES['MOZ_REPLACE_MALLOC'] = True
-
 DEFINES['MOZ_JEMALLOC_IMPL'] = True
 
 #XXX: PGO on Linux causes problems here
diff --git a/memory/replace/logalloc/replay/moz.build b/memory/replace/logalloc/replay/moz.build
index a74ae6549b38..8f862c4f3a16 100644
--- a/memory/replace/logalloc/replay/moz.build
+++ b/memory/replace/logalloc/replay/moz.build
@@ -21,5 +21,3 @@ USE_LIBS += [
 ]
 
 DISABLE_STL_WRAPPING = True
-
-DEFINES['MOZ_REPLACE_MALLOC'] = True