--- a/widget/PuppetWidget.cpp
+++ b/widget/PuppetWidget.cpp
@@ -113,16 +113,21 @@ PuppetWidget::Create(nsIWidget        *a
   PuppetWidget* parent = static_cast<PuppetWidget*>(aParent);
   if (parent) {
     parent->SetChild(this);
     mLayerManager = parent->GetLayerManager();
   }
   else {
     Resize(mBounds.x, mBounds.y, mBounds.width, mBounds.height, false);
   }
+  nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+  if (obs) {
+    mMemoryPressureObserver = new MemoryPressureObserver(this);
+    obs->AddObserver(mMemoryPressureObserver, "memory-pressure", false);
+  }
 
   return NS_OK;
 }
 
 void
 PuppetWidget::InitIMEState()
 {
   MOZ_ASSERT(mTabChild);
@@ -148,16 +153,19 @@ PuppetWidget::CreateChild(const nsIntRec
 }
 
 NS_IMETHODIMP
 PuppetWidget::Destroy()
 {
   Base::OnDestroy();
   Base::Destroy();
   mPaintTask.Revoke();
+  if (mMemoryPressureObserver) {
+    mMemoryPressureObserver->Remove();
+  }
   mChild = nullptr;
   if (mLayerManager) {
     mLayerManager->Destroy();
   }
   mLayerManager = nullptr;
   mTabChild = nullptr;
   return NS_OK;
 }
@@ -170,20 +178,16 @@ PuppetWidget::Show(bool aState)
 
   bool wasVisible = mVisible;
   mVisible = aState;
 
   if (mChild) {
     mChild->mVisible = aState;
   }
 
-  if (!mVisible && mLayerManager) {
-    mLayerManager->ClearCachedResources();
-  }
-
   if (!wasVisible && mVisible) {
     Resize(mBounds.width, mBounds.height, false);
     Invalidate(mBounds);
   }
 
   return NS_OK;
 }
 
@@ -1032,16 +1036,45 @@ NS_IMETHODIMP
 PuppetWidget::PaintTask::Run()
 {
   if (mWidget) {
     mWidget->Paint();
   }
   return NS_OK;
 }
 
+NS_IMPL_ISUPPORTS(PuppetWidget::MemoryPressureObserver, nsIObserver)
+
+NS_IMETHODIMP
+PuppetWidget::MemoryPressureObserver::Observe(nsISupports* aSubject,
+                                              const char* aTopic,
+                                              const char16_t* aData)
+{
+  if (!mWidget) {
+    return NS_OK;
+  }
+
+  if (strcmp("memory-pressure", aTopic) == 0) {
+    if (!mWidget->mVisible && mWidget->mLayerManager) {
+      mWidget->mLayerManager->ClearCachedResources();
+    }
+  }
+  return NS_OK;
+}
+
+void
+PuppetWidget::MemoryPressureObserver::Remove()
+{
+  nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+  if (obs) {
+    obs->RemoveObserver(this, "memory-pressure");
+  }
+  mWidget = nullptr;
+}
+
 bool
 PuppetWidget::NeedsPaint()
 {
   // e10s popups are handled by the parent process, so never should be painted here
   if (XRE_GetProcessType() == GeckoProcessType_Content &&
       Preferences::GetBool("browser.tabs.remote.desktopbehavior", false) &&
       mWindowType == eWindowType_popup) {
     NS_WARNING("Trying to paint an e10s popup in the child process!");

--- a/widget/PuppetWidget.h
+++ b/widget/PuppetWidget.h
@@ -274,28 +274,41 @@ private:
   public:
     NS_DECL_NSIRUNNABLE
     explicit PaintTask(PuppetWidget* widget) : mWidget(widget) {}
     void Revoke() { mWidget = nullptr; }
   private:
     PuppetWidget* mWidget;
   };
 
+  class MemoryPressureObserver : public nsIObserver {
+  public:
+    NS_DECL_ISUPPORTS
+    NS_DECL_NSIOBSERVER
+    explicit MemoryPressureObserver(PuppetWidget* aWidget) : mWidget(aWidget) {}
+    void Remove();
+  private:
+    virtual ~MemoryPressureObserver() {}
+    PuppetWidget* mWidget;
+  };
+  friend class MemoryPressureObserver;
+
   // TabChild normally holds a strong reference to this PuppetWidget
   // or its root ancestor, but each PuppetWidget also needs a
   // reference back to TabChild (e.g. to delegate nsIWidget IME calls
   // to chrome) So we hold a weak reference to TabChild here.  Since
   // it's possible for TabChild to outlive the PuppetWidget, we clear
   // this weak reference in Destroy()
   TabChild* mTabChild;
   // The "widget" to which we delegate events if we don't have an
   // event handler.
   nsRefPtr<PuppetWidget> mChild;
   nsIntRegion mDirtyRegion;
   nsRevocableEventPtr<PaintTask> mPaintTask;
+  nsRefPtr<MemoryPressureObserver> mMemoryPressureObserver;
   // XXX/cjones: keeping this around until we teach LayerManager to do
   // retained-content-only transactions
   mozilla::RefPtr<DrawTarget> mDrawTarget;
   // IME
   nsIMEUpdatePreference mIMEPreferenceOfParent;
   // Latest seqno received through events
   uint32_t mIMELastReceivedSeqno;
   // Chrome's seqno value when last blur occurred