--- a/dom/workers/ServiceWorkerRegistrar.cpp
+++ b/dom/workers/ServiceWorkerRegistrar.cpp
@@ -1113,50 +1113,57 @@ ServiceWorkerRegistrar::GetName(nsAStrin
 }
 
 NS_IMETHODIMP
 ServiceWorkerRegistrar::GetState(nsIPropertyBag**)
 {
   return NS_OK;
 }
 
+#define RELEASE_ASSERT_SUCCEEDED(rv, name) do { \
+    if (NS_FAILED(rv)) {                                                       \
+      if (rv == NS_ERROR_XPC_JAVASCRIPT_ERROR_WITH_DETAILS) {                  \
+        if (auto* context = CycleCollectedJSContext::Get()) {                  \
+          if (nsCOMPtr<nsIException> exn = context->GetPendingException()) {   \
+            nsAutoCString msg;                                                 \
+            if (NS_SUCCEEDED(exn->GetMessageMoz(msg))) {                       \
+              MOZ_CRASH_UNSAFE_PRINTF("Failed to get " name ": %s", msg.get());\
+            }                                                                  \
+          }                                                                    \
+        }                                                                      \
+      }                                                                        \
+                                                                               \
+      nsAutoCString errorName;                                                 \
+      GetErrorName(rv, errorName);                                             \
+      MOZ_CRASH_UNSAFE_PRINTF("Failed to get " name ": %s",                    \
+                              errorName.get());                                \
+    }                                                                          \
+  } while (0)
+
+
 nsCOMPtr<nsIAsyncShutdownClient>
 ServiceWorkerRegistrar::GetShutdownPhase() const
 {
-  nsCOMPtr<nsIAsyncShutdownService> svc = services::GetAsyncShutdown();
-  MOZ_RELEASE_ASSERT(svc);
-
-  nsCOMPtr<nsIAsyncShutdownClient> client;
-  nsresult rv = svc->GetProfileBeforeChange(getter_AddRefs(client));
+  nsresult rv;
+  nsCOMPtr<nsIAsyncShutdownService> svc = do_GetService(
+      "@mozilla.org/async-shutdown-service;1", &rv);
   // If this fails, something is very wrong on the JS side (or we're out of
   // memory), and there's no point in continuing startup. Include as much
   // information as possible in the crash report.
-  if (NS_FAILED(rv)) {
-    if (rv == NS_ERROR_XPC_JAVASCRIPT_ERROR_WITH_DETAILS) {
-      if (auto* context = CycleCollectedJSContext::Get()) {
-        if (nsCOMPtr<nsIException> exn = context->GetPendingException()) {
-          nsAutoCString msg;
-          if (NS_SUCCEEDED(exn->GetMessageMoz(msg))) {
-            MOZ_CRASH_UNSAFE_PRINTF("Failed to get profileBeforeChange shutdown blocker: %s",
-                                    msg.get());
+  RELEASE_ASSERT_SUCCEEDED(rv, "async shutdown service");
+
 
-          }
-        }
-      }
-    }
-
-    nsAutoCString errorName;
-    GetErrorName(rv, errorName);
-    MOZ_CRASH_UNSAFE_PRINTF("Failed to get profileBeforeChange shutdown blocker: %s",
-                            errorName.get());
-  }
-  MOZ_RELEASE_ASSERT(client);
+  nsCOMPtr<nsIAsyncShutdownClient> client;
+  rv = svc->GetProfileBeforeChange(getter_AddRefs(client));
+  RELEASE_ASSERT_SUCCEEDED(rv, "profileBeforeChange shutdown blocker");
   return Move(client);
 }
 
+#undef RELEASE_ASSERT_SUCCEEDED
+
 void
 ServiceWorkerRegistrar::Shutdown()
 {
   AssertIsOnBackgroundThread();
   MOZ_ASSERT(!mShuttingDown);
 
   mShuttingDown = true;
   MaybeScheduleShutdownCompleted();

--- a/js/xpconnect/loader/mozJSComponentLoader.cpp
+++ b/js/xpconnect/loader/mozJSComponentLoader.cpp
@@ -31,16 +31,17 @@
 #include "nsIJARURI.h"
 #include "nsNetUtil.h"
 #include "jsprf.h"
 #include "nsJSPrincipals.h"
 #include "nsJSUtils.h"
 #include "xpcprivate.h"
 #include "xpcpublic.h"
 #include "nsContentUtils.h"
+#include "nsReadableUtils.h"
 #include "nsXULAppAPI.h"
 #include "GeckoProfiler.h"
 #include "WrapperFactory.h"
 
 #include "AutoMemMap.h"
 #include "ScriptPreloader-inl.h"
 
 #include "mozilla/AddonPathService.h"
@@ -383,21 +384,39 @@ mozJSComponentLoader::LoadModule(FileLoc
     ModuleEntry* mod;
     if (mModules.Get(spec, &mod))
         return mod;
 
     dom::AutoJSAPI jsapi;
     jsapi.Init();
     JSContext* cx = jsapi.cx();
 
+    bool isCriticalModule = StringEndsWith(spec, NS_LITERAL_CSTRING("/nsAsyncShutdown.js"));
+
     nsAutoPtr<ModuleEntry> entry(new ModuleEntry(RootingContext::get(cx)));
-    RootedValue dummy(cx);
+    RootedValue exn(cx);
     rv = ObjectForLocation(info, file, &entry->obj, &entry->thisObjectKey,
-                           &entry->location, false, &dummy);
+                           &entry->location, isCriticalModule, &exn);
     if (NS_FAILED(rv)) {
+        // Temporary debugging assertion for bug 1403348:
+        if (isCriticalModule && !exn.isUndefined()) {
+            JSAutoCompartment ac(cx, xpc::PrivilegedJunkScope());
+            JS_WrapValue(cx, &exn);
+
+            nsAutoCString file;
+            uint32_t line;
+            uint32_t column;
+            nsAutoString msg;
+            nsContentUtils::ExtractErrorValues(cx, exn, file, &line, &column, msg);
+
+            NS_ConvertUTF16toUTF8 cMsg(msg);
+            MOZ_CRASH_UNSAFE_PRINTF("Failed to load module \"%s\": "
+                                    "[\"%s\" {file: \"%s\", line: %u}]",
+                                    spec.get(), cMsg.get(), file.get(), line);
+        }
         return nullptr;
     }
 
     nsCOMPtr<nsIComponentManager> cm;
     rv = NS_GetComponentManager(getter_AddRefs(cm));
     if (NS_FAILED(rv))
         return nullptr;