--- a/dom/workers/ServiceWorkerManager.cpp
+++ b/dom/workers/ServiceWorkerManager.cpp
@@ -1928,46 +1928,71 @@ ServiceWorkerManager::RemoveScope(nsTArr
 {
   aList.RemoveElement(aScope);
 }
 
 void
 ServiceWorkerManager::MaybeStartControlling(nsIDocument* aDoc)
 {
   AssertIsOnMainThread();
-  if (!Preferences::GetBool("dom.serviceWorkers.enabled")) {
-    return;
-  }
-
   nsRefPtr<ServiceWorkerRegistrationInfo> registration =
     GetServiceWorkerRegistrationInfo(aDoc);
   if (registration) {
     MOZ_ASSERT(!mControlledDocuments.Contains(aDoc));
     registration->StartControllingADocument();
     // Use the already_AddRefed<> form of Put to avoid the addref-deref since
     // we don't need the registration pointer in this function anymore.
     mControlledDocuments.Put(aDoc, registration.forget());
   }
 }
 
+class ServiceWorkerActivateAfterUnloadingJob MOZ_FINAL : public ServiceWorkerJob
+{
+  nsRefPtr<ServiceWorkerRegistrationInfo> mRegistration;
+public:
+  ServiceWorkerActivateAfterUnloadingJob(ServiceWorkerJobQueue* aQueue,
+                                         ServiceWorkerRegistrationInfo* aReg)
+    : ServiceWorkerJob(aQueue)
+    , mRegistration(aReg)
+  { }
+
+  void
+  Start()
+  {
+    if (mRegistration->mPendingUninstall) {
+      mRegistration->Clear();
+      nsRefPtr<ServiceWorkerManager> swm = ServiceWorkerManager::GetInstance();
+      swm->RemoveRegistration(mRegistration);
+    } else {
+      mRegistration->TryToActivate();
+    }
+
+    Done(NS_OK);
+  }
+};
+
 void
 ServiceWorkerManager::MaybeStopControlling(nsIDocument* aDoc)
 {
   MOZ_ASSERT(aDoc);
-  if (!Preferences::GetBool("dom.serviceWorkers.enabled")) {
-    return;
-  }
-
   nsRefPtr<ServiceWorkerRegistrationInfo> registration;
   mControlledDocuments.Remove(aDoc, getter_AddRefs(registration));
   // A document which was uncontrolled does not maintain that state itself, so
   // it will always call MaybeStopControlling() even if there isn't an
   // associated registration. So this check is required.
   if (registration) {
     registration->StopControllingADocument();
+    if (!registration->IsControllingDocuments()) {
+      ServiceWorkerJobQueue* queue = GetOrCreateJobQueue(registration->mScope);
+      // The remaining tasks touch registration->mPendingUninstall, so queue
+      // them up in a job.
+      nsRefPtr<ServiceWorkerActivateAfterUnloadingJob> job =
+        new ServiceWorkerActivateAfterUnloadingJob(queue, registration);
+      queue->Append(job);
+    }
   }
 }
 
 NS_IMETHODIMP
 ServiceWorkerManager::GetScopeForUrl(const nsAString& aUrl, nsAString& aScope)
 {
   nsCOMPtr<nsIURI> uri;
   nsresult rv = NS_NewURI(getter_AddRefs(uri), aUrl, nullptr, nullptr);

--- a/dom/workers/ServiceWorkerManager.h
+++ b/dom/workers/ServiceWorkerManager.h
@@ -285,22 +285,23 @@ public:
  * installation, querying and event dispatch of ServiceWorkers for all the
  * origins in the process.
  */
 class ServiceWorkerManager MOZ_FINAL
   : public nsIServiceWorkerManager
   , public nsIIPCBackgroundChildCreateCallback
 {
   friend class ActivationRunnable;
-  friend class ServiceWorkerRegistrationInfo;
-  friend class ServiceWorkerRegisterJob;
   friend class GetReadyPromiseRunnable;
   friend class GetRegistrationsRunnable;
   friend class GetRegistrationRunnable;
   friend class QueueFireUpdateFoundRunnable;
+  friend class ServiceWorkerActivateAfterUnloadingJob;
+  friend class ServiceWorkerRegisterJob;
+  friend class ServiceWorkerRegistrationInfo;
   friend class ServiceWorkerUnregisterJob;
 
 public:
   NS_DECL_ISUPPORTS
   NS_DECL_NSISERVICEWORKERMANAGER
   NS_DECL_NSIIPCBACKGROUNDCHILDCREATECALLBACK
   NS_DECLARE_STATIC_IID_ACCESSOR(NS_SERVICEWORKERMANAGER_IMPL_IID)
 
@@ -344,16 +345,18 @@ public:
   }
 
   ServiceWorkerRegistrationInfo*
   CreateNewRegistration(const nsCString& aScope, nsIPrincipal* aPrincipal);
 
   void
   RemoveRegistration(ServiceWorkerRegistrationInfo* aRegistration)
   {
+    MOZ_ASSERT(aRegistration);
+    MOZ_ASSERT(!aRegistration->IsControllingDocuments());
     MOZ_ASSERT(mServiceWorkerRegistrationInfos.Contains(aRegistration->mScope));
     ServiceWorkerManager::RemoveScope(mOrderedScopes, aRegistration->mScope);
     mServiceWorkerRegistrationInfos.Remove(aRegistration->mScope);
   }
 
   ServiceWorkerJobQueue*
   GetOrCreateJobQueue(const nsCString& aScope)
   {

--- a/dom/workers/test/serviceworkers/test_installation_simple.html
+++ b/dom/workers/test/serviceworkers/test_installation_simple.html
@@ -135,18 +135,17 @@
 
     window.onmessage = function(e) {
       if (e.data.type == "ready") {
         continueTest();
       } else if (e.data.type == "finish") {
         window.onmessage = null;
         // We have to make frame navigate away, otherwise it will call
         // MaybeStopControlling() when this document is unloaded. At that point
-        // the pref has been disabled, and so MaybeStopControlling() will just
-        // return since it is currently gated.
+        // the pref has been disabled, so the ServiceWorkerManager is not available.
         frame.setAttribute("src", new URL("about:blank").href);
         resolve();
       } else if (e.data.type == "check") {
         ok(e.data.status, e.data.msg);
       }
     }
     return p;
   }