diff --git a/startupcache/StartupCache.cpp b/startupcache/StartupCache.cpp
index cce1f77afb49..f00ff6b4228f 100644
--- a/startupcache/StartupCache.cpp
+++ b/startupcache/StartupCache.cpp
@@ -147,7 +147,26 @@ StartupCache::StartupCache()
       mPrefetchThread(nullptr) {}
 
 StartupCache::~StartupCache() {
+  if (mTimer) {
+    mTimer->Cancel();
+  }
+
+  // Generally, the in-memory table should be empty here,
+  // but an early shutdown means either mTimer didn't run
+  // or the write thread is still running.
   WaitOnWriteThread();
+  WaitOnPrefetchThread();
+
+  // If we shutdown quickly timer wont have fired. Instead of writing
+  // it on the main thread and block the shutdown we simply wont update
+  // the startup cache. Always do this if the file doesn't exist since
+  // we use it part of the package step.
+  if (!mCacheData.initialized() || ShouldCompactCache()) {
+    mDirty = true;
+    auto result = WriteToDisk();
+    Unused << NS_WARN_IF(result.isErr());
+  }
+
   UnregisterWeakMemoryReporter(this);
 }
 
@@ -594,25 +613,6 @@ void StartupCache::InvalidateCache(bool memoryOnly) {
   }
 }
 
-void StartupCache::MaybeInitShutdownWrite() {
-  if (mTimer) {
-    mTimer->Cancel();
-  }
-  gShutdownInitiated = true;
-
-  MaybeSpawnWriteThread();
-
-  // If we shutdown quickly timer wont have fired. Instead of writing
-  // it on the main thread and block the shutdown we simply wont update
-  // the startup cache. Always do this if the file doesn't exist since
-  // we use it part of the package step.
-  if (!mCacheData.initialized() || ShouldCompactCache()) {
-    mDirty = true;
-    auto result = WriteToDisk();
-    Unused << NS_WARN_IF(result.isErr());
-  }
-}
-
 void StartupCache::IgnoreDiskCache() {
   gIgnoreDiskCache = true;
   if (gStartupCache) gStartupCache->InvalidateCache();
@@ -690,28 +690,22 @@ void StartupCache::WriteTimeout(nsITimer* aTimer, void* aClosure) {
    * if the StartupCache object is valid.
    */
   StartupCache* startupCacheObj = static_cast<StartupCache*>(aClosure);
-  startupCacheObj->MaybeSpawnWriteThread();
-}
-
-/*
- * See StartupCache::WriteTimeout above - this is just the non-static body.
- */
-void StartupCache::MaybeSpawnWriteThread() {
-  if (mWrittenOnce || mWriteThread) {
+  if (startupCacheObj->mWrittenOnce) {
     return;
   }
 
-  if (mCacheData.initialized() && !ShouldCompactCache()) {
+  if (startupCacheObj->mCacheData.initialized() &&
+      !startupCacheObj->ShouldCompactCache()) {
     return;
   }
 
-  WaitOnPrefetchThread();
-  mStartupWriteInitiated = false;
-  mDirty = true;
-  mCacheData.reset();
-  mWriteThread = PR_CreateThread(PR_USER_THREAD, StartupCache::ThreadedWrite,
-                                 this, PR_PRIORITY_NORMAL, PR_GLOBAL_THREAD,
-                                 PR_JOINABLE_THREAD, 512 * 1024);
+  startupCacheObj->WaitOnPrefetchThread();
+  startupCacheObj->mStartupWriteInitiated = false;
+  startupCacheObj->mDirty = true;
+  startupCacheObj->mCacheData.reset();
+  startupCacheObj->mWriteThread = PR_CreateThread(
+      PR_USER_THREAD, StartupCache::ThreadedWrite, startupCacheObj,
+      PR_PRIORITY_NORMAL, PR_GLOBAL_THREAD, PR_JOINABLE_THREAD, 512 * 1024);
 }
 
 // We don't want to refcount StartupCache, so we'll just
@@ -726,7 +720,6 @@ nsresult StartupCacheListener::Observe(nsISupports* subject, const char* topic,
   if (strcmp(topic, NS_XPCOM_SHUTDOWN_OBSERVER_ID) == 0) {
     // Do not leave the thread running past xpcom shutdown
     sc->WaitOnWriteThread();
-    sc->WaitOnPrefetchThread();
     StartupCache::gShutdownInitiated = true;
   } else if (strcmp(topic, "startupcache-invalidate") == 0) {
     sc->InvalidateCache(data && nsCRT::strcmp(data, u"memoryOnly") == 0);
diff --git a/startupcache/StartupCache.h b/startupcache/StartupCache.h
index 2c1fca6239a5..2b10ac1a8ed9 100644
--- a/startupcache/StartupCache.h
+++ b/startupcache/StartupCache.h
@@ -163,10 +163,6 @@ class StartupCache : public nsIMemoryReporter {
   // Removes the cache file.
   void InvalidateCache(bool memoryOnly = false);
 
-  // For use during shutdown - this will write the startupcache's data
-  // to disk if the timer hasn't already gone off.
-  void MaybeInitShutdownWrite();
-
   // Signal that data should not be loaded from the cache file
   static void IgnoreDiskCache();
 
@@ -207,7 +203,6 @@ class StartupCache : public nsIMemoryReporter {
   void WaitOnWriteThread();
   void WaitOnPrefetchThread();
   void StartPrefetchMemoryThread();
-  void MaybeSpawnWriteThread();
 
   static nsresult InitSingleton();
   static void WriteTimeout(nsITimer* aTimer, void* aClosure);
diff --git a/xpcom/base/AppShutdown.cpp b/xpcom/base/AppShutdown.cpp
index ec013608a2b7..e57392b6957e 100644
--- a/xpcom/base/AppShutdown.cpp
+++ b/xpcom/base/AppShutdown.cpp
@@ -16,7 +16,6 @@
 #include "mozilla/CmdLineAndEnvUtils.h"
 #include "mozilla/PoisonIOInterposer.h"
 #include "mozilla/Printf.h"
-#include "mozilla/scache/StartupCache.h"
 #include "mozilla/StartupTimeline.h"
 #include "mozilla/StaticPrefs_toolkit.h"
 #include "mozilla/LateWriteChecks.h"
@@ -126,8 +125,6 @@ void AppShutdown::Init(AppShutdownMode aMode) {
   int32_t lateWriteChecksPref =
       StaticPrefs::toolkit_shutdown_lateWriteChecksStage();
   sLateWriteChecksPhase = GetShutdownPhaseFromPrefValue(lateWriteChecksPref);
-
-  scache::StartupCache::GetSingleton()->MaybeInitShutdownWrite();
 }
 
 void AppShutdown::MaybeFastShutdown(ShutdownPhase aPhase) {
diff --git a/xpcom/build/XPCOMInit.cpp b/xpcom/build/XPCOMInit.cpp
index f33fd92a8545..8be931bc8fbb 100644
--- a/xpcom/build/XPCOMInit.cpp
+++ b/xpcom/build/XPCOMInit.cpp
@@ -634,6 +634,7 @@ nsresult ShutdownXPCOM(nsIServiceManager* aServMgr) {
     gfxPlatform::ShutdownLayersIPC();
     mozilla::RemoteDecoderManagerChild::Shutdown();
 
+    mozilla::scache::StartupCache::DeleteSingleton();
     if (observerService) {
       mozilla::KillClearOnShutdown(ShutdownPhase::ShutdownThreads);
       observerService->NotifyObservers(
@@ -716,8 +717,6 @@ nsresult ShutdownXPCOM(nsIServiceManager* aServMgr) {
   mozilla::AppShutdown::MaybeFastShutdown(
       mozilla::ShutdownPhase::ShutdownPostLastCycleCollection);
 
-  mozilla::scache::StartupCache::DeleteSingleton();
-
   PROFILER_ADD_MARKER("Shutdown xpcom", OTHER);
 
   // Shutdown xpcom. This will release all loaders and cause others holding