--- a/browser/metro/shell/commandexecutehandler/CEHHelper.cpp
+++ b/browser/metro/shell/commandexecutehandler/CEHHelper.cpp
@@ -1,14 +1,15 @@
 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
  * You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "CEHHelper.h"
+#include <tlhelp32.h>
 
 #ifdef SHOW_CONSOLE
 #include <io.h> // _open_osfhandle
 #endif
 
 HANDLE sCon;
 LPCWSTR metroDX10Available = L"MetroD3DAvailable";
 
@@ -53,16 +54,63 @@ SetupConsole()
   int fd = _open_osfhandle(reinterpret_cast<intptr_t>(sCon), 0);
   fp = _fdopen(fd, "w");
   *stdout = *fp;
   setvbuf(stdout, nullptr, _IONBF, 0);
 }
 #endif
 
 bool
+IsImmersiveProcessDynamic(HANDLE process)
+{
+  HMODULE user32DLL = LoadLibraryW(L"user32.dll");
+  if (!user32DLL) {
+    return false;
+  }
+
+  typedef BOOL (WINAPI* IsImmersiveProcessFunc)(HANDLE process);
+  IsImmersiveProcessFunc IsImmersiveProcessPtr =
+    (IsImmersiveProcessFunc)GetProcAddress(user32DLL,
+                                           "IsImmersiveProcess");
+  if (!IsImmersiveProcessPtr) {
+    FreeLibrary(user32DLL);
+    return false;
+  }
+
+  BOOL bImmersiveProcess = IsImmersiveProcessPtr(process);
+  FreeLibrary(user32DLL);
+  return bImmersiveProcess;
+}
+
+bool
+IsImmersiveProcessRunning(const wchar_t *processName)
+{
+  bool exists = false;
+  PROCESSENTRY32W entry;
+  entry.dwSize = sizeof(PROCESSENTRY32W);
+
+  HANDLE snapshot = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, NULL);
+
+  if (Process32First(snapshot, &entry)) {
+    while (!exists && Process32Next(snapshot, &entry)) {
+      if (!_wcsicmp(entry.szExeFile, processName)) {
+        HANDLE process = OpenProcess(GENERIC_READ, FALSE, entry.th32ProcessID);
+        if (IsImmersiveProcessDynamic(process)) {
+          exists = true;
+        }
+        CloseHandle(process);
+      }
+    }
+  }
+
+  CloseHandle(snapshot);
+  return exists;
+}
+
+bool
 IsDX10Available()
 {
   DWORD isDX10Available;
   if (GetDWORDRegKey(metroDX10Available, isDX10Available)) {
     return isDX10Available;
   }
 
   HMODULE dxgiModule = LoadLibraryA("dxgi.dll");

--- a/browser/metro/shell/commandexecutehandler/CEHHelper.h
+++ b/browser/metro/shell/commandexecutehandler/CEHHelper.h
@@ -22,8 +22,10 @@ void Log(const wchar_t *fmt, ...);
 
 #if defined(SHOW_CONSOLE)
 void SetupConsole();
 #endif
 
 bool IsDX10Available();
 bool GetDWORDRegKey(LPCWSTR name, DWORD &value);
 bool SetDWORDRegKey(LPCWSTR name, DWORD value);
+bool IsImmersiveProcessDynamic(HANDLE process);
+bool IsImmersiveProcessRunning(const wchar_t *processName);

--- a/browser/metro/shell/commandexecutehandler/CommandExecuteHandler.cpp
+++ b/browser/metro/shell/commandexecutehandler/CommandExecuteHandler.cpp
@@ -28,19 +28,27 @@
 
 // Heartbeat timer duration used while waiting for an incoming request.
 #define HEARTBEAT_MSEC 1000
 // Total number of heartbeats we wait before giving up and shutting down.
 #define REQUEST_WAIT_TIMEOUT 30
 // Pulled from desktop browser's shell
 #define APP_REG_NAME L"Firefox"
 
+// If we have a restart request, attempt to wait up to RESTART_WAIT_TIMEOUT
+// until the previous instance closes.  We don't want to wait too long
+// because the browser could appear to randomly start for the user. We want
+// it to also be long enough so the browser has time to close.
+#define RESTART_WAIT_PER_RETRY 50
+#define RESTART_WAIT_TIMEOUT 38000
+
 static const WCHAR* kFirefoxExe = L"firefox.exe";
 static const WCHAR* kMetroFirefoxExe = L"firefox.exe";
 static const WCHAR* kDefaultMetroBrowserIDPathKey = L"FirefoxURL";
+static const WCHAR* kMetroRestartCmdLine = L"--metro-restart";
 
 static bool GetDefaultBrowserPath(CStringW& aPathBuffer);
 
 /*
  * Retrieve our module dir path.
  *
  * @aPathBuffer Buffer to fill
  */
@@ -90,16 +98,17 @@ public:
   CExecuteCommandVerb() :
     mRef(1),
     mShellItemArray(nullptr),
     mUnkSite(nullptr),
     mTargetIsFileSystemLink(false),
     mTargetIsDefaultBrowser(false),
     mTargetIsBrowser(false),
     mIsDesktopRequest(true),
+    mIsRestartMetroRequest(false),
     mRequestMet(false)
   {
   }
 
   bool RequestMet() { return mRequestMet; }
   long RefCount() { return mRef; }
 
   // IUnknown
@@ -135,17 +144,22 @@ public:
   {
     mKeyState = aKeyState;
     return S_OK;
   }
 
   IFACEMETHODIMP SetParameters(PCWSTR aParameters)
   {
     Log(L"SetParameters: '%s'", aParameters);
-    mParameters = aParameters;
+
+    if (_wcsicmp(aParameters, kMetroRestartCmdLine) == 0) {
+      mIsRestartMetroRequest = true;
+    } else {
+      mParameters = aParameters;
+    }
     return S_OK;
   }
 
   IFACEMETHODIMP SetPosition(POINT aPoint)
   { return S_OK; }
 
   IFACEMETHODIMP SetShowWindow(int aShowFlag)
   { return S_OK; }
@@ -396,16 +410,17 @@ private:
   CStringW mVerb;
   CStringW mTarget;
   CStringW mParameters;
   bool mTargetIsFileSystemLink;
   bool mTargetIsDefaultBrowser;
   bool mTargetIsBrowser;
   DWORD mKeyState;
   bool mIsDesktopRequest;
+  bool mIsRestartMetroRequest;
   bool mRequestMet;
 };
 
 /*
  * Retrieve the current default browser's path.
  *
  * @aPathBuffer Buffer to fill
  */
@@ -431,30 +446,25 @@ static bool GetDefaultBrowserPath(CStrin
 }
 
 /*
  * Retrieve the app model id of the firefox metro browser.
  *
  * @aPathBuffer Buffer to fill
  * @aCharLength Length of buffer to fill in characters
  */
-static bool GetDefaultBrowserAppModelID(WCHAR* aIDBuffer,
-                                        long aCharLength)
+template <size_t N>
+static bool GetDefaultBrowserAppModelID(WCHAR (&aIDBuffer)[N])
 {
-  if (!aIDBuffer || aCharLength <= 0)
-    return false;
-
-  memset(aIDBuffer, 0, (sizeof(WCHAR)*aCharLength));
-
   HKEY key;
   if (RegOpenKeyExW(HKEY_CLASSES_ROOT, kDefaultMetroBrowserIDPathKey,
                     0, KEY_READ, &key) != ERROR_SUCCESS) {
     return false;
   }
-  DWORD len = aCharLength * sizeof(WCHAR);
+  DWORD len = sizeof(aIDBuffer);
   memset(aIDBuffer, 0, len);
   if (RegQueryValueExW(key, L"AppUserModelID", nullptr, nullptr,
                        (LPBYTE)aIDBuffer, &len) != ERROR_SUCCESS || !len) {
     RegCloseKey(key);
     return false;
   }
   RegCloseKey(key);
   return true;
@@ -612,79 +622,132 @@ class AutoSetRequestMet
 public:
   explicit AutoSetRequestMet(bool* aFlag) :
     mFlag(aFlag) {}
   ~AutoSetRequestMet() { if (mFlag) *mFlag = true; }
 private:
   bool* mFlag;
 };
 
+static HRESULT
+PrepareActivationManager(CComPtr<IApplicationActivationManager> &activateMgr)
+{
+  HRESULT hr = activateMgr.CoCreateInstance(CLSID_ApplicationActivationManager, NULL, CLSCTX_LOCAL_SERVER);
+  if (FAILED(hr)) {
+    Log(L"CoCreateInstance failed, launching on desktop.");
+    return E_FAIL;
+  }
+
+  // Hand off focus rights to the out-of-process activation server. Without
+  // this the metro interface won't launch.
+  hr = CoAllowSetForegroundWindow(activateMgr, nullptr);
+  if (FAILED(hr)) {
+    Log(L"CoAllowSetForegroundWindow result %X", hr);
+    return E_FAIL;
+  }
+
+  return S_OK;
+}
+
+DWORD WINAPI
+DelayedExecuteThread(LPVOID param)
+{
+  Log(L"Starting delayed execute thread...");
+  bool &bRequestMet(*(bool*)param);
+  AutoSetRequestMet asrm(&bRequestMet);
+
+  CoInitialize(NULL);
+
+  CComPtr<IApplicationActivationManager> activateMgr;
+  if (FAILED(PrepareActivationManager(activateMgr))) {
+      Log(L"Warning: Could not prepare activation manager");
+  }
+
+  size_t currentWaitTime = 0;
+  while(currentWaitTime < RESTART_WAIT_TIMEOUT) {
+    if (!IsImmersiveProcessRunning(kMetroFirefoxExe))
+      break;
+    currentWaitTime += RESTART_WAIT_PER_RETRY;
+    Sleep(RESTART_WAIT_PER_RETRY);
+  }
+
+  Log(L"Done waiting, getting app ID");
+  // Activate the application as long as we can obtian the appModelID
+  WCHAR appModelID[256];
+  if (GetDefaultBrowserAppModelID(appModelID)) {
+    Log(L"Activating application");
+    DWORD processID;
+    HRESULT hr = activateMgr->ActivateApplication(appModelID, L"", AO_NONE, &processID);
+    if (SUCCEEDED(hr)) {
+      Log(L"Activate application succeeded");
+    } else {
+      Log(L"Activate application failed! (%x)", hr);
+    }
+  }
+
+  CoUninitialize();
+  return 0;
+}
+
 IFACEMETHODIMP CExecuteCommandVerb::Execute()
 {
   Log(L"Execute()");
 
+  if (!mTarget.GetLength()) {
+    // We shut down when this flips to true
+    mRequestMet = true;
+    return E_FAIL;
+  }
+
+  if (mIsRestartMetroRequest) {
+    HANDLE thread = CreateThread(NULL, 0, DelayedExecuteThread, &mRequestMet, 0, NULL);
+    CloseHandle(thread);
+    return S_OK;
+  }
+
   // We shut down when this flips to true
   AutoSetRequestMet asrm(&mRequestMet);
 
-  if (!mTarget.GetLength()) {
-    return E_FAIL;
-  }
-
   // Launch on the desktop
   if (mIsDesktopRequest) {
     LaunchDesktopBrowser();
     return S_OK;
   }
 
-  // Launch into Metro
-  IApplicationActivationManager* activateMgr = nullptr;
-  DWORD processID;
-  if (FAILED(CoCreateInstance(CLSID_ApplicationActivationManager, nullptr,
-                              CLSCTX_LOCAL_SERVER,
-                              IID_IApplicationActivationManager,
-                              (void**)&activateMgr))) {
-    Log(L"CoCreateInstance failed, launching on desktop.");
-    LaunchDesktopBrowser();
-    return S_OK;
+  CComPtr<IApplicationActivationManager> activateMgr;
+  if (!PrepareActivationManager(activateMgr)) {
+      LaunchDesktopBrowser();
+      return S_OK;
   }
-  
+
   HRESULT hr;
   WCHAR appModelID[256];
-  if (!GetDefaultBrowserAppModelID(appModelID, (sizeof(appModelID)/sizeof(WCHAR)))) {
+  if (!GetDefaultBrowserAppModelID(appModelID)) {
     Log(L"GetDefaultBrowserAppModelID failed, launching on desktop.");
-    activateMgr->Release();
     LaunchDesktopBrowser();
     return S_OK;
   }
 
-  // Hand off focus rights to the out-of-process activation server. Without
-  // this the metro interface won't launch.
-  hr = CoAllowSetForegroundWindow(activateMgr, nullptr);
-  if (FAILED(hr)) {
-    Log(L"CoAllowSetForegroundWindow result %X", hr);
-    activateMgr->Release();
-    return false;
-  }
-
   Log(L"Metro Launch: verb:%s appid:%s params:%s", mVerb, appModelID, mTarget); 
 
+
   // shortcuts to the application
+  DWORD processID;
   if (mTargetIsDefaultBrowser) {
     hr = activateMgr->ActivateApplication(appModelID, L"", AO_NONE, &processID);
     Log(L"ActivateApplication result %X", hr);
   // files
   } else if (mTargetIsFileSystemLink) {
     hr = activateMgr->ActivateForFile(appModelID, mShellItemArray, mVerb, &processID);
     Log(L"ActivateForFile result %X", hr);
   // protocols
   } else {
     hr = activateMgr->ActivateForProtocol(appModelID, mShellItemArray, &processID);
     Log(L"ActivateForProtocol result %X", hr);
   }
-  activateMgr->Release();
   return S_OK;
 }
 
 class ClassFactory : public IClassFactory 
 {
 public:
   ClassFactory(IUnknown *punkObject);
   ~ClassFactory();