diff --git a/mozilla/modules/ipc/common/ipcConfig.h b/mozilla/modules/ipc/common/ipcConfig.h
index df381a8b15d..952d40b2257 100644
--- a/mozilla/modules/ipc/common/ipcConfig.h
+++ b/mozilla/modules/ipc/common/ipcConfig.h
@@ -48,6 +48,7 @@
 #define IPC_WINDOW_NAME               "Mozilla:IPCWindow"
 #define IPC_CLIENT_WINDOW_CLASS       "Mozilla:IPCAppWindowClass"
 #define IPC_CLIENT_WINDOW_NAME_PREFIX "Mozilla:IPCAppWindow:"
+#define IPC_SYNC_EVENT_NAME           "Local\\MozillaIPCSyncEvent"
 #define IPC_DAEMON_APP_NAME           "mozipcd.exe"
 #define IPC_PATH_SEP_CHAR             '\\'
 
diff --git a/mozilla/modules/ipc/daemon/ipcdUnix.cpp b/mozilla/modules/ipc/daemon/ipcdUnix.cpp
index 832b851ee9d..df340029afb 100644
--- a/mozilla/modules/ipc/daemon/ipcdUnix.cpp
+++ b/mozilla/modules/ipc/daemon/ipcdUnix.cpp
@@ -383,8 +383,10 @@ int main(int argc, char **argv)
     else
         socket_path = argv[1];
 
-    if (!InitDaemonDir(socket_path))
+    if (!InitDaemonDir(socket_path)) {
+        PR_Close(listenFD);
         return 0;
+    }
 
     addr.local.family = PR_AF_LOCAL;
     PL_strncpyz(addr.local.path, socket_path, sizeof(addr.local.path));
diff --git a/mozilla/modules/ipc/daemon/ipcdWin.cpp b/mozilla/modules/ipc/daemon/ipcdWin.cpp
index f047d6a9939..930b9fe3b55 100644
--- a/mozilla/modules/ipc/daemon/ipcdWin.cpp
+++ b/mozilla/modules/ipc/daemon/ipcdWin.cpp
@@ -200,7 +200,7 @@ IPC_SendMessageNow(ipcClient *client, const ipcMessage *msg)
 //-----------------------------------------------------------------------------
 
 static LRESULT CALLBACK
-ipcWindowProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
+WindowProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
 {
     LOG(("got message [msg=%x wparam=%x lparam=%x]\n", uMsg, wParam, lParam));
 
@@ -230,6 +230,47 @@ ipcWindowProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
     return DefWindowProc(hWnd, uMsg, wParam, lParam);
 }
 
+//-----------------------------------------------------------------------------
+// daemon startup synchronization
+//-----------------------------------------------------------------------------
+
+static HANDLE ipcSyncEvent;
+
+static PRBool
+AcquireLock()
+{
+    ipcSyncEvent = CreateEvent(NULL, FALSE, FALSE,
+                               IPC_SYNC_EVENT_NAME);
+    if (!ipcSyncEvent) {
+        LOG(("CreateEvent failed [%u]\n", GetLastError()));
+        return PR_FALSE;
+    }
+
+    if (ipcSyncEvent) {
+        // check to see if event already existed prior to this call.
+        if (GetLastError() == ERROR_ALREADY_EXISTS) {
+            LOG(("  lock already set; exiting...\n"));
+            return PR_FALSE;
+        }
+    }
+    
+    LOG(("  acquired lock\n"));
+    return PR_TRUE;
+}
+
+static void
+ReleaseLock()
+{
+    if (ipcSyncEvent) {
+        CloseHandle(ipcSyncEvent);
+        ipcSyncEvent = NULL;
+    }
+}
+
+//-----------------------------------------------------------------------------
+// main
+//-----------------------------------------------------------------------------
+
 int
 main(int argc, char **argv)
 {
@@ -238,6 +279,9 @@ main(int argc, char **argv)
 #endif
     LOG(("daemon started...\n"));
 
+    if (!AcquireLock())
+        return 0;
+
     ipcClients = ipcClientArray;
     ipcClientCount = 0;
 
@@ -246,7 +290,7 @@ main(int argc, char **argv)
     //
     WNDCLASS wc;
     memset(&wc, 0, sizeof(wc));
-    wc.lpfnWndProc = ipcWindowProc;
+    wc.lpfnWndProc = WindowProc;
     wc.lpszClassName = IPC_WINDOW_CLASS;
 
     RegisterClass(&wc);
@@ -270,6 +314,8 @@ main(int argc, char **argv)
     while (GetMessage(&msg, ipcHwnd, 0, 0))
         DispatchMessage(&msg);
 
+    ReleaseLock();
+
     LOG(("exiting\n"));
     return 0;
 }