--- a/dom/ipc/ContentParent.cpp
+++ b/dom/ipc/ContentParent.cpp
@@ -1501,16 +1501,18 @@ void
 ContentParent::ShutDownProcess(ShutDownMethod aMethod)
 {
     // Shutting down by sending a shutdown message works differently than the
     // other methods. We first call Shutdown() in the child. After the child is
     // ready, it calls FinishShutdown() on us. Then we close the channel.
     if (aMethod == SEND_SHUTDOWN_MESSAGE) {
         if (mIPCOpen && !mShutdownPending && SendShutdown()) {
             mShutdownPending = true;
+            // Start the force-kill timer if we haven't already.
+            StartForceKillTimer();
         }
 
         // If call was not successful, the channel must have been broken
         // somehow, and we will clean up the error in ActorDestroy.
         return;
     }
 
     using mozilla::dom::quota::QuotaManager;
@@ -1918,18 +1920,26 @@ ContentParent::NotifyTabDestroying(PBrow
     ++mNumDestroyingTabs;
     if (mNumDestroyingTabs != numLiveTabs) {
         return;
     }
 
     // We're dying now, so prevent this content process from being
     // recycled during its shutdown procedure.
     MarkAsDead();
-
-    MOZ_ASSERT(!mForceKillTimer);
+    StartForceKillTimer();
+}
+
+void
+ContentParent::StartForceKillTimer()
+{
+    if (mForceKillTimer || !mIPCOpen) {
+        return;
+    }
+
     int32_t timeoutSecs =
         Preferences::GetInt("dom.ipc.tabs.shutdownTimeoutSecs", 5);
     if (timeoutSecs > 0) {
         mForceKillTimer = do_CreateInstance("@mozilla.org/timer;1");
         MOZ_ASSERT(mForceKillTimer);
         mForceKillTimer->InitWithFuncCallback(ContentParent::ForceKillTimerCallback,
                                               this,
                                               timeoutSecs * 1000,

--- a/dom/ipc/ContentParent.h
+++ b/dom/ipc/ContentParent.h
@@ -460,16 +460,19 @@ 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();
 
+    // Start the force-kill timer on shutdown.
+    void StartForceKillTimer();
+
     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;