diff --git a/browser/app/moz.build b/browser/app/moz.build
index 5a35fd07e612..bc1f24325b22 100644
--- a/browser/app/moz.build
+++ b/browser/app/moz.build
@@ -56,6 +56,11 @@ if CONFIG['MOZ_SANDBOX'] and CONFIG['OS_ARCH'] == 'WINNT':
         'sandbox_s',
     ]
 
+    DELAYLOAD_DLLS += [
+        'winmm.dll',
+        'user32.dll',
+    ]
+
 # Control the default heap size.
 # This is the heap returned by GetProcessHeap().
 # As we use the CRT heap, the default size is too large and wastes VM.
diff --git a/browser/app/nsBrowserApp.cpp b/browser/app/nsBrowserApp.cpp
index 2ef2f8705ae9..4764a51a95a6 100644
--- a/browser/app/nsBrowserApp.cpp
+++ b/browser/app/nsBrowserApp.cpp
@@ -322,6 +322,20 @@ sizeof(XPCOM_DLL) - 1))
 
 int main(int argc, char* argv[], char* envp[])
 {
+  mozilla::TimeStamp start = mozilla::TimeStamp::Now();
+
+#ifdef HAS_DLL_BLOCKLIST
+  DllBlocklist_Initialize();
+
+#ifdef DEBUG
+  // In order to be effective against AppInit DLLs, the blocklist must be
+  // initialized before user32.dll is loaded into the process (bug 932100).
+  if (GetModuleHandleA("user32.dll")) {
+    fprintf(stderr, "DLL blocklist was unable to intercept AppInit DLLs.\n");
+  }
+#endif
+#endif
+
 #ifdef MOZ_BROWSER_CAN_BE_CONTENTPROC
   // We are launching as a content process, delegate to the appropriate
   // main
@@ -349,22 +363,9 @@ int main(int argc, char* argv[], char* envp[])
   }
 #endif
 
-  mozilla::TimeStamp start = mozilla::TimeStamp::Now();
 
   nsIFile *xreDirectory;
 
-#ifdef HAS_DLL_BLOCKLIST
-  DllBlocklist_Initialize();
-
-#ifdef DEBUG
-  // In order to be effective against AppInit DLLs, the blocklist must be
-  // initialized before user32.dll is loaded into the process (bug 932100).
-  if (GetModuleHandleA("user32.dll")) {
-    fprintf(stderr, "DLL blocklist was unable to intercept AppInit DLLs.\n");
-  }
-#endif
-#endif
-
   nsresult rv = InitXPCOMGlue(argv[0], &xreDirectory);
   if (NS_FAILED(rv)) {
     return 255;
diff --git a/ipc/app/MozillaRuntimeMain.cpp b/ipc/app/MozillaRuntimeMain.cpp
index 67b636333145..3f977e4623ee 100644
--- a/ipc/app/MozillaRuntimeMain.cpp
+++ b/ipc/app/MozillaRuntimeMain.cpp
@@ -1,12 +1,19 @@
-/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
- * vim: sw=4 ts=4 et :
- * This Source Code Form is subject to the terms of the Mozilla Public
+/* -*- 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/. */
 
 #include "../contentproc/plugin-container.cpp"
- 
+
+#include "mozilla/WindowsDllBlocklist.h"
+
 int
-main(int argc, char *argv[]) {
-    return content_process_main(argc, argv);
+main(int argc, char *argv[])
+{
+#ifdef HAS_DLL_BLOCKLIST
+  DllBlocklist_Initialize();
+#endif
+
+  return content_process_main(argc, argv);
 }
diff --git a/ipc/app/moz.build b/ipc/app/moz.build
index 6c89083e5b8c..6fc4828a8c92 100644
--- a/ipc/app/moz.build
+++ b/ipc/app/moz.build
@@ -37,15 +37,30 @@ if CONFIG['OS_TARGET'] != 'Android':
         'rlz',
     ]
 
-if CONFIG['MOZ_SANDBOX'] and CONFIG['OS_ARCH'] == 'WINNT':
-    # For sandbox includes and the include dependencies those have
-    LOCAL_INCLUDES += [
-        '/security/sandbox/chromium',
-        '/security/sandbox/chromium-shim',
+# DELAYLOAD_DLLS in this block ensures that the DLL blocklist is functional
+if CONFIG['OS_ARCH'] == 'WINNT':
+    DELAYLOAD_DLLS += [
+        'nss3.dll',
     ]
 
-    USE_LIBS += [
-        'sandbox_s',
+    if CONFIG['MOZ_SANDBOX']:
+        # For sandbox includes and the include dependencies those have
+        LOCAL_INCLUDES += [
+            '/security/sandbox/chromium',
+            '/security/sandbox/chromium-shim',
+        ]
+
+        USE_LIBS += [
+            'sandbox_s',
+        ]
+
+        DELAYLOAD_DLLS += [
+            'winmm.dll',
+            'user32.dll',
+        ]
+
+    DELAYLOAD_DLLS += [
+        'xul.dll',
     ]
 
 if CONFIG['MOZ_SANDBOX'] and CONFIG['OS_TARGET'] in ('Linux', 'Android'):
diff --git a/js/xpconnect/shell/moz.build b/js/xpconnect/shell/moz.build
index 4352c2bcbbb5..f1a4a192ea94 100644
--- a/js/xpconnect/shell/moz.build
+++ b/js/xpconnect/shell/moz.build
@@ -31,6 +31,7 @@ if CONFIG['_MSC_VER']:
     # a console application.
     WIN32_EXE_LDFLAGS += ['-ENTRY:wmainCRTStartup']
 
+# DELAYLOAD_DLLS in this block ensure that the DLL blocklist initializes
 if CONFIG['OS_ARCH'] == 'WINNT':
     RCINCLUDE = 'xpcshell.rc'
 
@@ -45,6 +46,15 @@ if CONFIG['OS_ARCH'] == 'WINNT':
             'sandbox_s',
         ]
 
+        DELAYLOAD_DLLS += [
+            'winmm.dll',
+            'user32.dll',
+        ]
+
+    DELAYLOAD_DLLS += [
+        'xul.dll',
+    ]
+
 CFLAGS += CONFIG['TK_CFLAGS']
 CXXFLAGS += CONFIG['TK_CFLAGS']
 OS_LIBS += CONFIG['TK_LIBS']
diff --git a/mozglue/build/WindowsDllBlocklist.cpp b/mozglue/build/WindowsDllBlocklist.cpp
index 3d9bf5156a20..24e359adf4c4 100644
--- a/mozglue/build/WindowsDllBlocklist.cpp
+++ b/mozglue/build/WindowsDllBlocklist.cpp
@@ -243,6 +243,7 @@ static const int kUser32BeforeBlocklistParameterLen =
   sizeof(kUser32BeforeBlocklistParameter) - 1;
 
 static DWORD sThreadLoadingXPCOMModule;
+static bool sBlocklistInitAttempted;
 static bool sBlocklistInitFailed;
 static bool sUser32BeforeBlocklist;
 
@@ -756,9 +757,16 @@ WindowsDllInterceptor NtDllIntercept;
 MFBT_API void
 DllBlocklist_Initialize()
 {
+  if (sBlocklistInitAttempted) {
+    return;
+  }
+  sBlocklistInitAttempted = true;
+
   if (GetModuleHandleA("user32.dll")) {
     sUser32BeforeBlocklist = true;
   }
+  // Catch any missing DELAYLOADS for user32.dll
+  MOZ_ASSERT(!sUser32BeforeBlocklist);
 
   NtDllIntercept.Init("ntdll.dll");
 
diff --git a/toolkit/xre/nsEmbedFunctions.cpp b/toolkit/xre/nsEmbedFunctions.cpp
index c5d5945498d1..a81168c3682f 100644
--- a/toolkit/xre/nsEmbedFunctions.cpp
+++ b/toolkit/xre/nsEmbedFunctions.cpp
@@ -304,10 +304,6 @@ XRE_InitChildProcess(int aArgc,
   NS_ENSURE_ARG_POINTER(aArgv[0]);
   MOZ_ASSERT(aChildData);
 
-#ifdef HAS_DLL_BLOCKLIST
-  DllBlocklist_Initialize();
-#endif
-
 #ifdef MOZ_JPROF
   // Call the code to install our handler
   setupProfilingStuff();