diff --git a/dom/plugins/PluginInstanceChild.cpp b/dom/plugins/PluginInstanceChild.cpp
index 58f117ea7c04..d7ad55b35a7a 100644
--- a/dom/plugins/PluginInstanceChild.cpp
+++ b/dom/plugins/PluginInstanceChild.cpp
@@ -84,9 +84,6 @@ const int kFlashWMUSERMessageThrottleDelayMs = 5;
 
 #define NS_OOPP_DOUBLEPASS_MSGID TEXT("MozDoublePassMsg")
 
-#ifndef WM_MOUSEHWHEEL
-#define WM_MOUSEHWHEEL                    0x020E
-#endif
 #elif defined(XP_MACOSX)
 #include <ApplicationServices/ApplicationServices.h>
 #endif // defined(XP_MACOSX)
@@ -1060,21 +1057,6 @@ PluginInstanceChild::PluginWindowProc(HWND hWnd,
     if (message == WM_MOUSEACTIVATE)
         self->CallPluginGotFocus();
 
-    // Prevent lockups due to plugins making rpc calls when the parent
-    // is making a synchronous SendMessage call to the child window. Add
-    // more messages as needed.
-    if ((InSendMessageEx(NULL)&(ISMEX_REPLIED|ISMEX_SEND)) == ISMEX_SEND) {
-        switch(message) {
-            case WM_KILLFOCUS:
-            case WM_MOUSEHWHEEL:
-            case WM_MOUSEWHEEL:
-            case WM_HSCROLL:
-            case WM_VSCROLL:
-            ReplyMessage(0);
-            break;
-        }
-    }
-
     if (message == WM_USER+1 &&
         (self->mQuirks & PluginInstanceChild::QUIRK_FLASH_THROTTLE_WMUSER_EVENTS)) {
         self->FlashThrottleMessage(hWnd, message, wParam, lParam, true);
diff --git a/dom/plugins/PluginModuleChild.cpp b/dom/plugins/PluginModuleChild.cpp
index 2f221b3119c1..ad1463e66378 100644
--- a/dom/plugins/PluginModuleChild.cpp
+++ b/dom/plugins/PluginModuleChild.cpp
@@ -66,6 +66,12 @@
 
 using namespace mozilla::plugins;
 
+#if defined(XP_WIN)
+#ifndef WM_MOUSEHWHEEL
+#define WM_MOUSEHWHEEL     0x020E
+#endif
+#endif
+
 namespace {
 PluginModuleChild* gInstance = nsnull;
 }
@@ -82,6 +88,7 @@ PluginModuleChild::PluginModuleChild() :
 #endif
 #ifdef OS_WIN
   , mNestedEventHook(NULL)
+  , mGlobalCallWndProcHook(NULL)
 #endif
 {
     NS_ASSERTION(!gInstance, "Something terribly wrong here!");
@@ -488,7 +495,7 @@ PluginModuleChild::AnswerNP_Shutdown(NPError *rv)
     memset(&mFunctions, 0, sizeof(mFunctions));
 
 #ifdef OS_WIN
-    ResetNestedInputEventHook();
+    ResetEventHooks();
 #endif
 
     return true;
@@ -1496,7 +1503,7 @@ PluginModuleChild::AnswerNP_Initialize(NativeThreadId* tid, NPError* _retval)
 #endif
 
 #ifdef OS_WIN
-    SetNestedInputEventHook();
+    SetEventHooks();
 #endif
 
 #if defined(OS_LINUX)
@@ -1875,6 +1882,59 @@ PluginModuleChild::ExitedCall()
     mIncallPumpingStack.TruncateLength(len - 1);
 }
 
+LRESULT CALLBACK
+PluginModuleChild::CallWindowProcHook(int nCode, WPARAM wParam, LPARAM lParam)
+{
+    // Trap and reply to anything we recognize as the source of a
+    // potential send message deadlock.
+    if (nCode >= 0 &&
+        (InSendMessageEx(NULL)&(ISMEX_REPLIED|ISMEX_SEND)) == ISMEX_SEND) {
+        CWPSTRUCT* pCwp = reinterpret_cast<CWPSTRUCT*>(lParam);
+        switch(pCwp->message) {
+            // Sync messages we can reply to:
+            case WM_SETFOCUS:
+            case WM_KILLFOCUS:
+            case WM_MOUSEHWHEEL:
+            case WM_MOUSEWHEEL:
+            case WM_HSCROLL:
+            case WM_VSCROLL:
+            case WM_CONTEXTMENU:
+            case WM_IME_SETCONTEXT:
+            case WM_WINDOWPOSCHANGED:
+                ReplyMessage(0);
+            break;
+            // Sync message that can't be handled:
+            case WM_WINDOWPOSCHANGING:
+            case WM_DESTROY:
+            case WM_PAINT:
+            break;
+            // Everything else:
+            default: {
+#ifdef DEBUG
+              nsCAutoString log("Child plugin module received untrapped ");
+              log.AppendLiteral("synchronous message for window. msg=");
+              char szTmp[40];
+              sprintf(szTmp, "0x%06X", pCwp->message);
+              log.Append(szTmp);
+              log.AppendLiteral(" hwnd=");
+              sprintf(szTmp, "0x%08X", pCwp->hwnd);
+              log.Append(szTmp);
+              PRUnichar className[256] = { 0 };
+              if (GetClassNameW(pCwp->hwnd, className,
+                                sizeof(className)/sizeof(PRUnichar)) > 0) {
+                  log.AppendLiteral(" class='");
+                  log.Append(NS_ConvertUTF16toUTF8((PRUnichar*)className));
+                  log.AppendLiteral("'");
+              }
+              NS_WARNING(log.get());
+#endif
+            }
+        }
+    }
+
+    return CallNextHookEx(NULL, nCode, wParam, lParam);
+}
+
 LRESULT CALLBACK
 PluginModuleChild::NestedInputEventHook(int nCode, WPARAM wParam, LPARAM lParam)
 {
@@ -1893,29 +1953,38 @@ PluginModuleChild::NestedInputEventHook(int nCode, WPARAM wParam, LPARAM lParam)
 }
 
 void
-PluginModuleChild::SetNestedInputEventHook()
+PluginModuleChild::SetEventHooks()
 {
     NS_ASSERTION(!mNestedEventHook,
         "mNestedEventHook already setup in call to SetNestedInputEventHook?");
+    NS_ASSERTION(!mGlobalCallWndProcHook,
+        "mGlobalCallWndProcHook already setup in call to CallWindowProcHook?");
 
     PLUGIN_LOG_DEBUG(("%s", FULLFUNCTION));
 
-    // WH_GETMESSAGE hooks are triggered by peek message calls in parent due to
-    // attached message queues, resulting in stomped in-process ipc calls.  So
-    // we use a filter hook specific to dialogs, menus, and scroll bars to kick
-    // things off.
+    // WH_MSGFILTER event hook for detecting modal loops in the child.
     mNestedEventHook = SetWindowsHookEx(WH_MSGFILTER,
                                         NestedInputEventHook,
                                         NULL,
                                         GetCurrentThreadId());
+
+    // WH_CALLWNDPROC event hook for trapping sync messages sent from
+    // parent that can cause deadlocks.
+    mGlobalCallWndProcHook = SetWindowsHookEx(WH_CALLWNDPROC,
+                                              CallWindowProcHook,
+                                              NULL,
+                                              GetCurrentThreadId());
 }
 
 void
-PluginModuleChild::ResetNestedInputEventHook()
+PluginModuleChild::ResetEventHooks()
 {
     PLUGIN_LOG_DEBUG(("%s", FULLFUNCTION));
     if (mNestedEventHook)
         UnhookWindowsHookEx(mNestedEventHook);
     mNestedEventHook = NULL;
+    if (mGlobalCallWndProcHook)
+        UnhookWindowsHookEx(mGlobalCallWndProcHook);
+    mGlobalCallWndProcHook = NULL;
 }
 #endif
diff --git a/dom/plugins/PluginModuleChild.h b/dom/plugins/PluginModuleChild.h
index f0a5d9eb453c..ab3a05aace5a 100644
--- a/dom/plugins/PluginModuleChild.h
+++ b/dom/plugins/PluginModuleChild.h
@@ -323,9 +323,13 @@ private:
     static LRESULT CALLBACK NestedInputEventHook(int code,
                                                  WPARAM wParam,
                                                  LPARAM lParam);
-    void SetNestedInputEventHook();
-    void ResetNestedInputEventHook();
+    static LRESULT CALLBACK CallWindowProcHook(int code,
+                                               WPARAM wParam,
+                                               LPARAM lParam);
+    void SetEventHooks();
+    void ResetEventHooks();
     HHOOK mNestedEventHook;
+    HHOOK mGlobalCallWndProcHook;
 #endif
 };