diff --git a/widget/android/AndroidBridge.cpp b/widget/android/AndroidBridge.cpp
index 4eb9d39e4c5..0c7740c7ceb 100644
--- a/widget/android/AndroidBridge.cpp
+++ b/widget/android/AndroidBridge.cpp
@@ -512,9 +512,9 @@ AndroidBridge::ShowAlertNotification(const nsAString& aImageUrl,
                                      const nsAString& aAlertName,
                                      nsIPrincipal* aPrincipal)
 {
-    if (nsAppShell::gAppShell && aAlertListener) {
+    if (aAlertListener) {
         // This will remove any observers already registered for this id
-        nsAppShell::gAppShell->PostEvent(AndroidGeckoEvent::MakeAddObserver(aAlertName, aAlertListener));
+        nsAppShell::PostEvent(AndroidGeckoEvent::MakeAddObserver(aAlertName, aAlertListener));
     }
 
     nsAutoString host;
@@ -1706,15 +1706,17 @@ AndroidBridge::PumpMessageLoop()
 
 NS_IMETHODIMP nsAndroidBridge::GetBrowserApp(nsIAndroidBrowserApp * *aBrowserApp)
 {
-    if (nsAppShell::gAppShell)
-        nsAppShell::gAppShell->GetBrowserApp(aBrowserApp);
+    nsAppShell* const appShell = nsAppShell::Get();
+    if (appShell)
+        appShell->GetBrowserApp(aBrowserApp);
     return NS_OK;
 }
 
 NS_IMETHODIMP nsAndroidBridge::SetBrowserApp(nsIAndroidBrowserApp *aBrowserApp)
 {
-    if (nsAppShell::gAppShell)
-        nsAppShell::gAppShell->SetBrowserApp(aBrowserApp);
+    nsAppShell* const appShell = nsAppShell::Get();
+    if (appShell)
+        appShell->SetBrowserApp(aBrowserApp);
     return NS_OK;
 }
 
diff --git a/widget/android/AndroidContentController.cpp b/widget/android/AndroidContentController.cpp
index 6840091567b..de90012f05c 100644
--- a/widget/android/AndroidContentController.cpp
+++ b/widget/android/AndroidContentController.cpp
@@ -77,7 +77,7 @@ AndroidContentController::HandleSingleTap(const CSSPoint& aPoint,
 
         CSSIntPoint rounded = RoundedToInt(point);
         nsCString data = nsPrintfCString("{ \"x\": %d, \"y\": %d }", rounded.x, rounded.y);
-        nsAppShell::gAppShell->PostEvent(AndroidGeckoEvent::MakeBroadcastEvent(
+        nsAppShell::PostEvent(AndroidGeckoEvent::MakeBroadcastEvent(
                 NS_LITERAL_CSTRING("Gesture:SingleTap"), data));
     }
 
diff --git a/widget/android/AndroidJNI.cpp b/widget/android/AndroidJNI.cpp
index d128d2da23f..35e0b3f2c34 100644
--- a/widget/android/AndroidJNI.cpp
+++ b/widget/android/AndroidJNI.cpp
@@ -61,8 +61,7 @@ NS_EXPORT void JNICALL
 Java_org_mozilla_gecko_GeckoAppShell_notifyGeckoOfEvent(JNIEnv *jenv, jclass jc, jobject event)
 {
     // poke the appshell
-    if (nsAppShell::gAppShell)
-        nsAppShell::gAppShell->PostEvent(AndroidGeckoEvent::MakeFromJavaObject(jenv, event));
+    nsAppShell::PostEvent(AndroidGeckoEvent::MakeFromJavaObject(jenv, event));
 }
 
 NS_EXPORT void JNICALL
@@ -342,7 +341,7 @@ Java_org_mozilla_gecko_gfx_NativePanZoomController_handleTouchEvent(JNIEnv* env,
     MultiTouchInput input = wrapper->MakeMultiTouchInput(nsWindow::TopWindow());
     delete wrapper;
 
-    if (input.mType < 0 || !nsAppShell::gAppShell) {
+    if (input.mType < 0) {
         return false;
     }
 
@@ -350,7 +349,7 @@ Java_org_mozilla_gecko_gfx_NativePanZoomController_handleTouchEvent(JNIEnv* env,
     uint64_t blockId;
     nsEventStatus status = controller->ReceiveInputEvent(input, &guid, &blockId);
     if (status != nsEventStatus_eConsumeNoDefault) {
-        nsAppShell::gAppShell->PostEvent(AndroidGeckoEvent::MakeApzInputEvent(input, guid, blockId, status));
+        nsAppShell::PostEvent(AndroidGeckoEvent::MakeApzInputEvent(input, guid, blockId, status));
     }
     return true;
 }
diff --git a/widget/android/PrefsHelper.h b/widget/android/PrefsHelper.h
index 06ad8e7e3a5..020bf5588ac 100644
--- a/widget/android/PrefsHelper.h
+++ b/widget/android/PrefsHelper.h
@@ -26,7 +26,9 @@ struct PrefsHelper
                              bool observe)
     {
         MOZ_ASSERT(NS_IsMainThread());
-        MOZ_ASSERT(nsAppShell::gAppShell);
+
+        nsAppShell* const appShell = nsAppShell::Get();
+        MOZ_ASSERT(appShell);
 
         nsTArray<jni::Object::LocalRef> namesRefArray(prefNames.GetElements());
         const size_t len = namesRefArray.Length();
@@ -48,7 +50,7 @@ struct PrefsHelper
         }
 
         nsIAndroidBrowserApp* browserApp = nullptr;
-        nsAppShell::gAppShell->GetBrowserApp(&browserApp);
+        appShell->GetBrowserApp(&browserApp);
         MOZ_ASSERT(browserApp);
 
         if (observe) {
@@ -63,10 +65,12 @@ struct PrefsHelper
     static void RemovePrefsObserver(int32_t requestId)
     {
         MOZ_ASSERT(NS_IsMainThread());
-        MOZ_ASSERT(nsAppShell::gAppShell);
+
+        nsAppShell* const appShell = nsAppShell::Get();
+        MOZ_ASSERT(appShell);
 
         nsIAndroidBrowserApp* browserApp = nullptr;
-        nsAppShell::gAppShell->GetBrowserApp(&browserApp);
+        appShell->GetBrowserApp(&browserApp);
         MOZ_ASSERT(browserApp);
 
         browserApp->RemovePreferenceObservers(requestId);
diff --git a/widget/android/nsAppShell.cpp b/widget/android/nsAppShell.cpp
index 88dfeaa37a6..6798285f417 100644
--- a/widget/android/nsAppShell.cpp
+++ b/widget/android/nsAppShell.cpp
@@ -75,7 +75,8 @@ PRLogModuleInfo *gWidgetLog = nullptr;
 nsIGeolocationUpdate *gLocationCallback = nullptr;
 nsAutoPtr<mozilla::AndroidGeckoEvent> gLastSizeChange;
 
-nsAppShell *nsAppShell::gAppShell = nullptr;
+nsAppShell* nsAppShell::sAppShell;
+StaticMutex nsAppShell::sAppShellLock;
 
 NS_IMPL_ISUPPORTS_INHERITED(nsAppShell, nsBaseAppShell, nsIObserver)
 
@@ -185,7 +186,10 @@ public:
 
 nsAppShell::nsAppShell()
 {
-    gAppShell = this;
+    {
+        StaticMutexAutoLock lock(sAppShellLock);
+        sAppShell = this;
+    }
 
     if (!XRE_IsParentProcess()) {
         return;
@@ -217,7 +221,10 @@ nsAppShell::~nsAppShell()
         NS_WARNING("Discarded event on shutdown");
     }
 
-    gAppShell = nullptr;
+    {
+        StaticMutexAutoLock lock(sAppShellLock);
+        sAppShell = nullptr;
+    }
 
     if (sPowerManagerService) {
         sPowerManagerService->RemoveWakeLockListener(sWakeLockListener);
@@ -398,7 +405,11 @@ public:
 void
 nsAppShell::PostEvent(AndroidGeckoEvent* event)
 {
-    mEventQueue.Post(mozilla::MakeUnique<LegacyGeckoEvent>(event));
+    mozilla::StaticMutexAutoLock lock(sAppShellLock);
+    if (!sAppShell) {
+        return;
+    }
+    sAppShell->mEventQueue.Post(mozilla::MakeUnique<LegacyGeckoEvent>(event));
 }
 
 void
@@ -410,7 +421,7 @@ nsAppShell::LegacyGeckoEvent::Run()
 
     switch (curEvent->Type()) {
     case AndroidGeckoEvent::NATIVE_POKE:
-        nsAppShell::gAppShell->NativeEventCallback();
+        nsAppShell::Get()->NativeEventCallback();
         break;
 
     case AndroidGeckoEvent::SENSOR_EVENT: {
@@ -519,19 +530,19 @@ nsAppShell::LegacyGeckoEvent::Run()
     }
 
     case AndroidGeckoEvent::THUMBNAIL: {
-        if (!nsAppShell::gAppShell->mBrowserApp)
+        if (!nsAppShell::Get()->mBrowserApp)
             break;
 
         int32_t tabId = curEvent->MetaState();
         const nsTArray<nsIntPoint>& points = curEvent->Points();
         RefCountedJavaObject* buffer = curEvent->ByteBuffer();
-        RefPtr<ThumbnailRunnable> sr = new ThumbnailRunnable(nsAppShell::gAppShell->mBrowserApp, tabId, points, buffer);
+        RefPtr<ThumbnailRunnable> sr = new ThumbnailRunnable(nsAppShell::Get()->mBrowserApp, tabId, points, buffer);
         MessageLoop::current()->PostIdleTask(FROM_HERE, NewRunnableMethod(sr.get(), &ThumbnailRunnable::Run));
         break;
     }
 
     case AndroidGeckoEvent::ZOOMEDVIEW: {
-        if (!nsAppShell::gAppShell->mBrowserApp)
+        if (!nsAppShell::Get()->mBrowserApp)
             break;
         int32_t tabId = curEvent->MetaState();
         const nsTArray<nsIntPoint>& points = curEvent->Points();
@@ -541,7 +552,7 @@ nsAppShell::LegacyGeckoEvent::Run()
 
         nsCOMPtr<nsIDOMWindow> domWindow;
         nsCOMPtr<nsIBrowserTab> tab;
-        nsAppShell::gAppShell->mBrowserApp->GetBrowserTab(tabId, getter_AddRefs(tab));
+        nsAppShell::Get()->mBrowserApp->GetBrowserTab(tabId, getter_AddRefs(tab));
         if (!tab) {
             NS_ERROR("Can't find tab!");
             break;
@@ -577,7 +588,7 @@ nsAppShell::LegacyGeckoEvent::Run()
             break;
 
         nsCOMPtr<nsIUITelemetryObserver> obs;
-        nsAppShell::gAppShell->mBrowserApp->GetUITelemetryObserver(getter_AddRefs(obs));
+        nsAppShell::Get()->mBrowserApp->GetUITelemetryObserver(getter_AddRefs(obs));
         if (!obs)
             break;
 
@@ -594,7 +605,7 @@ nsAppShell::LegacyGeckoEvent::Run()
             break;
 
         nsCOMPtr<nsIUITelemetryObserver> obs;
-        nsAppShell::gAppShell->mBrowserApp->GetUITelemetryObserver(getter_AddRefs(obs));
+        nsAppShell::Get()->mBrowserApp->GetUITelemetryObserver(getter_AddRefs(obs));
         if (!obs)
             break;
 
@@ -610,7 +621,7 @@ nsAppShell::LegacyGeckoEvent::Run()
             break;
 
         nsCOMPtr<nsIUITelemetryObserver> obs;
-        nsAppShell::gAppShell->mBrowserApp->GetUITelemetryObserver(getter_AddRefs(obs));
+        nsAppShell::Get()->mBrowserApp->GetUITelemetryObserver(getter_AddRefs(obs));
         if (!obs)
             break;
 
@@ -713,7 +724,7 @@ nsAppShell::LegacyGeckoEvent::Run()
     case AndroidGeckoEvent::CALL_OBSERVER:
     {
         nsCOMPtr<nsIObserver> observer;
-        nsAppShell::gAppShell->mObserversHash.Get(curEvent->Characters(), getter_AddRefs(observer));
+        nsAppShell::Get()->mObserversHash.Get(curEvent->Characters(), getter_AddRefs(observer));
 
         if (observer) {
             observer->Observe(nullptr, NS_ConvertUTF16toUTF8(curEvent->CharactersExtra()).get(),
@@ -726,11 +737,11 @@ nsAppShell::LegacyGeckoEvent::Run()
     }
 
     case AndroidGeckoEvent::REMOVE_OBSERVER:
-        nsAppShell::gAppShell->mObserversHash.Remove(curEvent->Characters());
+        nsAppShell::Get()->mObserversHash.Remove(curEvent->Characters());
         break;
 
     case AndroidGeckoEvent::ADD_OBSERVER:
-        nsAppShell::gAppShell->AddObserver(curEvent->Characters(), curEvent->Observer());
+        nsAppShell::Get()->AddObserver(curEvent->Characters(), curEvent->Observer());
         break;
 
     case AndroidGeckoEvent::LOW_MEMORY:
@@ -850,7 +861,7 @@ nsAppShell::LegacyGeckoEvent::PostTo(mozilla::LinkedList<Event>& queue)
 
         case AndroidGeckoEvent::MOTION_EVENT:
         case AndroidGeckoEvent::APZ_INPUT_EVENT:
-            if (nsAppShell::gAppShell->mAllowCoalescingTouches) {
+            if (sAppShell->mAllowCoalescingTouches) {
                 Event* const event = queue.getLast();
                 if (event && event->HasSameTypeAs(this) && ae->CanCoalesceWith(
                         static_cast<LegacyGeckoEvent*>(event)->ae.get())) {
@@ -891,18 +902,21 @@ namespace mozilla {
 
 bool ProcessNextEvent()
 {
-    if (!nsAppShell::gAppShell) {
+    nsAppShell* const appShell = nsAppShell::Get();
+    if (!appShell) {
         return false;
     }
 
-    return nsAppShell::gAppShell->ProcessNextNativeEvent(true) ? true : false;
+    return appShell->ProcessNextNativeEvent(true) ? true : false;
 }
 
 void NotifyEvent()
 {
-    if (nsAppShell::gAppShell) {
-        nsAppShell::gAppShell->NotifyNativeEvent();
+    nsAppShell* const appShell = nsAppShell::Get();
+    if (!appShell) {
+        return;
     }
+    appShell->NotifyNativeEvent();
 }
 
 }
diff --git a/widget/android/nsAppShell.h b/widget/android/nsAppShell.h
index 02377ff9e8f..b7472014ff5 100644
--- a/widget/android/nsAppShell.h
+++ b/widget/android/nsAppShell.h
@@ -10,6 +10,7 @@
 #include "mozilla/LinkedList.h"
 #include "mozilla/Monitor.h"
 #include "mozilla/Move.h"
+#include "mozilla/StaticMutex.h"
 #include "mozilla/UniquePtr.h"
 #include "mozilla/unused.h"
 #include "mozilla/jni/Natives.h"
@@ -69,7 +70,11 @@ public:
         void Run() override { return lambda(); }
     };
 
-    static nsAppShell *gAppShell;
+    static nsAppShell* Get()
+    {
+        MOZ_ASSERT(NS_IsMainThread());
+        return sAppShell;
+    }
 
     nsAppShell();
 
@@ -84,26 +89,32 @@ public:
     // Post a subclass of Event.
     // e.g. PostEvent(mozilla::MakeUnique<MyEvent>());
     template<typename T, typename D>
-    void PostEvent(mozilla::UniquePtr<T, D>&& event)
+    static void PostEvent(mozilla::UniquePtr<T, D>&& event)
     {
-        mEventQueue.Post(mozilla::Move(event));
+        mozilla::StaticMutexAutoLock lock(sAppShellLock);
+        if (!sAppShell) {
+            return;
+        }
+        sAppShell->mEventQueue.Post(mozilla::Move(event));
     }
 
     // Post a event that will call a lambda
     // e.g. PostEvent([=] { /* do something */ });
     template<typename T>
-    void PostEvent(T&& lambda)
+    static void PostEvent(T&& lambda)
     {
-        mEventQueue.Post(mozilla::MakeUnique<LambdaEvent<T>>(
+        mozilla::StaticMutexAutoLock lock(sAppShellLock);
+        if (!sAppShell) {
+            return;
+        }
+        sAppShell->mEventQueue.Post(mozilla::MakeUnique<LambdaEvent<T>>(
                 mozilla::Move(lambda)));
     }
 
-    void PostEvent(mozilla::AndroidGeckoEvent* event);
+    static void PostEvent(mozilla::AndroidGeckoEvent* event);
 
     void ResendLastResizeEvent(nsWindow* aDest);
 
-    void OnResume() {}
-
     void SetBrowserApp(nsIAndroidBrowserApp* aBrowserApp) {
         mBrowserApp = aBrowserApp;
     }
@@ -113,6 +124,9 @@ public:
     }
 
 protected:
+    static nsAppShell* sAppShell;
+    static mozilla::StaticMutex sAppShellLock;
+
     virtual ~nsAppShell();
 
     nsresult AddObserver(const nsAString &aObserverKey, nsIObserver *aObserver);
@@ -190,7 +204,7 @@ public:
     template<class Functor>
     static void OnNativeCall(Functor&& call)
     {
-        nsAppShell::gAppShell->PostEvent(mozilla::Move(call));
+        nsAppShell::PostEvent(mozilla::Move(call));
     }
 };
 
diff --git a/widget/android/nsWindow.cpp b/widget/android/nsWindow.cpp
index 9f3180b6976..a9cdfb1488c 100644
--- a/widget/android/nsWindow.cpp
+++ b/widget/android/nsWindow.cpp
@@ -230,7 +230,7 @@ public:
             // can get a head start on opening our window.
             return aCall();
         }
-        return nsAppShell::gAppShell->PostEvent(mozilla::MakeUnique<
+        return nsAppShell::PostEvent(mozilla::MakeUnique<
                 WindowEvent<Functor>>(mozilla::Move(aCall)));
     }
 
@@ -432,7 +432,7 @@ class nsWindow::GLControllerSupport final
             finished = true;
             lock.NotifyAll();
         };
-        nsAppShell::gAppShell->PostEvent(
+        nsAppShell::PostEvent(
                 mozilla::MakeUnique<GLControllerEvent>(
                 new nsAppShell::LambdaEvent<decltype(callAndNotify)>(
                 mozilla::Move(callAndNotify))));
@@ -473,7 +473,7 @@ public:
             return aCall();
         }
 
-        nsAppShell::gAppShell->PostEvent(
+        nsAppShell::PostEvent(
                 mozilla::MakeUnique<GLControllerEvent>(
                 new GeckoViewSupport::WindowEvent<Functor>(
                 mozilla::Move(aCall))));
@@ -491,7 +491,7 @@ public:
     ~GLControllerSupport()
     {
         GLController::GlobalRef glController(mozilla::Move(mGLController));
-        nsAppShell::gAppShell->PostEvent([glController] {
+        nsAppShell::PostEvent([glController] {
             GLControllerSupport::DisposeNative(GLController::LocalRef(
                         jni::GetGeckoThreadEnv(), glController));
         });
@@ -1220,7 +1220,7 @@ nsWindow::BringToFront()
     }
 
     // force a window resize
-    nsAppShell::gAppShell->ResendLastResizeEvent(newTop);
+    nsAppShell::Get()->ResendLastResizeEvent(newTop);
     RedrawAll();
 }
 
@@ -2289,7 +2289,7 @@ nsWindow::GeckoViewSupport::PostFlushIMEChanges(FlushChangesFlag aFlags)
     // Keep a strong reference to the window to keep 'this' alive.
     RefPtr<nsWindow> window(&this->window);
 
-    nsAppShell::gAppShell->PostEvent([this, window, aFlags] {
+    nsAppShell::PostEvent([this, window, aFlags] {
         if (!window->Destroyed()) {
             FlushIMEChanges(aFlags);
         }
@@ -2501,7 +2501,7 @@ nsWindow::GeckoViewSupport::SetInputContext(const InputContext& aContext,
     RefPtr<nsWindow> window(&this->window);
     mIMEUpdatingContext = true;
 
-    nsAppShell::gAppShell->PostEvent([this, window] {
+    nsAppShell::PostEvent([this, window] {
         mIMEUpdatingContext = false;
         if (window->Destroyed()) {
             return;