--- a/dom/ipc/ContentParent.cpp
+++ b/dom/ipc/ContentParent.cpp
@@ -111,16 +111,17 @@
 #include "nsIMutable.h"
 #include "nsIObserverService.h"
 #include "nsIPresShell.h"
 #include "nsIScriptError.h"
 #include "nsISiteSecurityService.h"
 #include "nsISpellChecker.h"
 #include "nsIStyleSheet.h"
 #include "nsISupportsPrimitives.h"
+#include "nsITimer.h"
 #include "nsIURIFixup.h"
 #include "nsIWindowWatcher.h"
 #include "nsIXULRuntime.h"
 #include "nsMemoryInfoDumper.h"
 #include "nsMemoryReporterManager.h"
 #include "nsServiceManagerUtils.h"
 #include "nsStyleSheetService.h"
 #include "nsThreadUtils.h"
@@ -1763,19 +1764,19 @@ struct DelayedDeleteContentParentTask : 
     nsRefPtr<ContentParent> mObj;
 };
 
 }
 
 void
 ContentParent::ActorDestroy(ActorDestroyReason why)
 {
-    if (mForceKillTask) {
-        mForceKillTask->Cancel();
-        mForceKillTask = nullptr;
+    if (mForceKillTimer) {
+        mForceKillTimer->Cancel();
+        mForceKillTimer = nullptr;
     }
 
     // Signal shutdown completion regardless of error state,
     // so we can finish waiting in the xpcom-shutdown observer.
     mIPCOpen = false;
 
     if (why == NormalShutdown && !mCalledClose) {
         // If we shut down normally but haven't called Close, assume somebody
@@ -1917,24 +1918,26 @@ ContentParent::NotifyTabDestroying(PBrow
     if (mNumDestroyingTabs != numLiveTabs) {
         return;
     }
 
     // We're dying now, so prevent this content process from being
     // recycled during its shutdown procedure.
     MarkAsDead();
 
-    MOZ_ASSERT(!mForceKillTask);
+    MOZ_ASSERT(!mForceKillTimer);
     int32_t timeoutSecs =
         Preferences::GetInt("dom.ipc.tabs.shutdownTimeoutSecs", 5);
     if (timeoutSecs > 0) {
-        MessageLoop::current()->PostDelayedTask(
-            FROM_HERE,
-            mForceKillTask = NewRunnableMethod(this, &ContentParent::KillHard),
-            timeoutSecs * 1000);
+        mForceKillTimer = do_CreateInstance("@mozilla.org/timer;1");
+        MOZ_ASSERT(mForceKillTimer);
+        mForceKillTimer->InitWithFuncCallback(ContentParent::ForceKillTimerCallback,
+                                              this,
+                                              timeoutSecs * 1000,
+                                              nsITimer::TYPE_ONE_SHOT);
     }
 }
 
 void
 ContentParent::NotifyTabDestroyed(PBrowserParent* aTab,
                                   bool aNotifiedDestroying)
 {
     if (aNotifiedDestroying) {
@@ -1984,17 +1987,16 @@ ContentParent::GetTestShellSingleton()
 }
 
 void
 ContentParent::InitializeMembers()
 {
     mSubprocess = nullptr;
     mChildID = gContentChildID++;
     mGeolocationWatchID = -1;
-    mForceKillTask = nullptr;
     mNumDestroyingTabs = 0;
     mIsAlive = true;
     mSendPermissionUpdates = false;
     mSendDataStoreInfos = false;
     mCalledClose = false;
     mCalledCloseWithError = false;
     mCalledKillHard = false;
     mCreatedPairedMinidumps = false;
@@ -2162,18 +2164,18 @@ ContentParent::ContentParent(ContentPare
                  false  /* Send registered chrome */);
 
     ContentProcessManager::GetSingleton()->AddContentProcess(this);
 }
 #endif  // MOZ_NUWA_PROCESS
 
 ContentParent::~ContentParent()
 {
-    if (mForceKillTask) {
-        mForceKillTask->Cancel();
+    if (mForceKillTimer) {
+        mForceKillTimer->Cancel();
     }
 
     if (OtherProcess())
         base::CloseProcessHandle(OtherProcess());
 
     NS_ASSERTION(NS_IsMainThread(), "Wrong thread!");
 
     // We should be removed from all these lists in ActorDestroy.
@@ -3154,27 +3156,34 @@ ContentParent::AllocPRemoteSpellcheckEng
 
 bool
 ContentParent::DeallocPRemoteSpellcheckEngineParent(PRemoteSpellcheckEngineParent *parent)
 {
     delete parent;
     return true;
 }
 
+/* static */ void
+ContentParent::ForceKillTimerCallback(nsITimer* aTimer, void* aClosure)
+{
+    auto self = static_cast<ContentParent*>(aClosure);
+    self->KillHard();
+}
+
 void
 ContentParent::KillHard()
 {
     // On Windows, calling KillHard multiple times causes problems - the
     // process handle becomes invalid on the first call, causing a second call
     // to crash our process - more details in bug 890840.
     if (mCalledKillHard) {
         return;
     }
     mCalledKillHard = true;
-    mForceKillTask = nullptr;
+    mForceKillTimer = nullptr;
 
 #if defined(MOZ_CRASHREPORTER) && !defined(MOZ_B2G)
     if (ManagedPCrashReporterParent().Length() > 0) {
         CrashReporterParent* crashReporter =
             static_cast<CrashReporterParent*>(ManagedPCrashReporterParent()[0]);
 
         // We're about to kill the child process associated with this
         // ContentParent. Something has gone wrong to get us here,

--- a/dom/ipc/ContentParent.h
+++ b/dom/ipc/ContentParent.h
@@ -28,16 +28,17 @@
 #define CHILD_PROCESS_SHUTDOWN_MESSAGE NS_LITERAL_STRING("child-process-shutdown")
 
 class mozIApplication;
 class nsConsoleService;
 class nsICycleCollectorLogSink;
 class nsIDOMBlob;
 class nsIDumpGCAndCCLogsCallback;
 class nsIMemoryReporter;
+class nsITimer;
 class ParentIdleListener;
 
 namespace mozilla {
 class PRemoteSpellcheckEngineParent;
 
 namespace ipc {
 class OptionalURIParams;
 class PFileDescriptorSetParent;
@@ -459,16 +460,18 @@ private:
      * is an abnormal shutdown (e.g. a crash).
      */
     void ShutDownProcess(ShutDownMethod aMethod);
 
     // Perform any steps necesssary to gracefully shtudown the message
     // manager and null out mMessageManager.
     void ShutDownMessageManager();
 
+    static void ForceKillTimerCallback(nsITimer* aTimer, void* aClosure);
+
     PCompositorParent*
     AllocPCompositorParent(mozilla::ipc::Transport* aTransport,
                            base::ProcessId aOtherProcess) MOZ_OVERRIDE;
     PImageBridgeParent*
     AllocPImageBridgeParent(mozilla::ipc::Transport* aTransport,
                             base::ProcessId aOtherProcess) MOZ_OVERRIDE;
 
     PSharedBufferManagerParent*
@@ -785,17 +788,17 @@ private:
      * expensive.
      */
     nsString mAppName;
 
     // After we initiate shutdown, we also start a timer to ensure
     // that even content processes that are 100% blocked (say from
     // SIGSTOP), are still killed eventually.  This task enforces that
     // timer.
-    CancelableTask* mForceKillTask;
+    nsCOMPtr<nsITimer> mForceKillTimer;
     // How many tabs we're waiting to finish their destruction
     // sequence.  Precisely, how many TabParents have called
     // NotifyTabDestroying() but not called NotifyTabDestroyed().
     int32_t mNumDestroyingTabs;
     // True only while this is ready to be used to host remote tabs.
     // This must not be used for new purposes after mIsAlive goes to
     // false, but some previously scheduled IPC traffic may still pass
     // through.