diff --git a/dom/ipc/ContentParent.cpp b/dom/ipc/ContentParent.cpp
index 1f4e837c6c3c..dd334d26bc65 100755
--- a/dom/ipc/ContentParent.cpp
+++ b/dom/ipc/ContentParent.cpp
@@ -1606,6 +1606,25 @@ ContentParent::OnChannelError()
     PContentParent::OnChannelError();
 }
 
+void
+ContentParent::OnBeginSyncTransaction() {
+    if (XRE_GetProcessType() == GeckoProcessType_Default) {
+        nsCOMPtr<nsIConsoleService> console(do_GetService(NS_CONSOLESERVICE_CONTRACTID));
+        JSContext *cx = nsContentUtils::GetCurrentJSContext();
+        if (console && cx) {
+            nsAutoString filename;
+            uint32_t lineno = 0;
+            nsJSUtils::GetCallingLocation(cx, filename, &lineno);
+            nsCOMPtr<nsIScriptError> error(do_CreateInstance(NS_SCRIPTERROR_CONTRACTID));
+            error->Init(NS_LITERAL_STRING("unsafe CPOW usage"), filename, EmptyString(),
+                        lineno, 0, nsIScriptError::warningFlag, "chrome javascript");
+            console->LogMessage(error);
+        } else {
+            NS_WARNING("Unsafe synchronous IPC message");
+        }
+    }
+}
+
 void
 ContentParent::OnChannelConnected(int32_t pid)
 {
diff --git a/dom/ipc/ContentParent.h b/dom/ipc/ContentParent.h
index f6b723836c5b..4101b9b84b19 100644
--- a/dom/ipc/ContentParent.h
+++ b/dom/ipc/ContentParent.h
@@ -253,6 +253,8 @@ public:
 
     virtual void OnChannelError() MOZ_OVERRIDE;
 
+    virtual void OnBeginSyncTransaction() MOZ_OVERRIDE;
+
     virtual PCrashReporterParent*
     AllocPCrashReporterParent(const NativeThreadId& tid,
                               const uint32_t& processType) MOZ_OVERRIDE;
diff --git a/ipc/glue/MessageChannel.cpp b/ipc/glue/MessageChannel.cpp
index 2a4f87ed3811..9ca1a10fd764 100644
--- a/ipc/glue/MessageChannel.cpp
+++ b/ipc/glue/MessageChannel.cpp
@@ -719,6 +719,9 @@ MessageChannel::Send(Message* aMsg, Message* aReply)
     AssertWorkerThread();
     mMonitor->AssertNotCurrentThreadOwns();
 
+    if (mCurrentTransaction == 0)
+        mListener->OnBeginSyncTransaction();
+
 #ifdef OS_WIN
     SyncStackFrame frame(this, false);
 #endif
diff --git a/ipc/glue/MessageLink.h b/ipc/glue/MessageLink.h
index 42535c02c73b..069024c7799e 100644
--- a/ipc/glue/MessageLink.h
+++ b/ipc/glue/MessageLink.h
@@ -88,6 +88,10 @@ class MessageListener
     virtual void OnExitedCall() {
         NS_RUNTIMEABORT("default impl shouldn't be invoked");
     }
+    /* This callback is called when a sync message is sent that begins a new IPC transaction
+       (i.e., when it is not part of an existing sequence of nested messages). */
+    virtual void OnBeginSyncTransaction() {
+    }
     virtual RacyInterruptPolicy MediateInterruptRace(const Message& parent,
                                                      const Message& child)
     {