diff --git a/content/events/public/nsIPrivateDOMEvent.h b/content/events/public/nsIPrivateDOMEvent.h
index cf4b4e2504e..1b451c1dafc 100644
--- a/content/events/public/nsIPrivateDOMEvent.h
+++ b/content/events/public/nsIPrivateDOMEvent.h
@@ -67,6 +67,8 @@ public:
   NS_IMETHOD IsDispatchStopped(PRBool* aIsDispatchPrevented) = 0;
   NS_IMETHOD GetInternalNSEvent(nsEvent** aNSEvent) = 0;
   NS_IMETHOD HasOriginalTarget(PRBool* aResult)=0;
+  NS_IMETHOD IsTrustedEvent(PRBool* aResult)=0;
+  NS_IMETHOD SetTrusted(PRBool aTrusted)=0;
 };
 
 extern nsresult NS_NewDOMEvent(nsIDOMEvent** aInstancePtrResult, nsIPresContext* aPresContext, nsEvent *aEvent);
diff --git a/content/events/src/nsDOMEvent.cpp b/content/events/src/nsDOMEvent.cpp
index d094061d464..d006c11c717 100644
--- a/content/events/src/nsDOMEvent.cpp
+++ b/content/events/src/nsDOMEvent.cpp
@@ -151,11 +151,13 @@ nsDOMEvent::nsDOMEvent(nsIPresContext* aPresContext, nsEvent* aEvent,
   NS_INIT_REFCNT();
 
   mPresContext = aPresContext;
+  mEventIsTrusted = PR_FALSE;
 
   NS_IF_ADDREF(mPresContext);
 
   if (aEvent) {
     mEvent = aEvent;
+    mEventIsTrusted = PR_TRUE;
   }
   else {
     mEventIsInternal = PR_TRUE;
@@ -375,6 +377,20 @@ nsDOMEvent::HasOriginalTarget(PRBool* aResult)
   return NS_OK;
 }
 
+NS_IMETHODIMP
+nsDOMEvent::IsTrustedEvent(PRBool* aResult)
+{
+  *aResult = mEventIsTrusted;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsDOMEvent::SetTrusted(PRBool aTrusted)
+{
+  mEventIsTrusted = aTrusted;
+  return NS_OK;
+}
+
 NS_IMETHODIMP
 nsDOMEvent::GetEventPhase(PRUint16* aEventPhase)
 {
diff --git a/content/events/src/nsDOMEvent.h b/content/events/src/nsDOMEvent.h
index 2f652be01ca..8c61fd7af3b 100644
--- a/content/events/src/nsDOMEvent.h
+++ b/content/events/src/nsDOMEvent.h
@@ -195,6 +195,8 @@ public:
   NS_IMETHOD    IsDispatchStopped(PRBool* aIsDispatchStopped);
   NS_IMETHOD    GetInternalNSEvent(nsEvent** aNSEvent);
   NS_IMETHOD    HasOriginalTarget(PRBool* aResult);
+  NS_IMETHOD    IsTrustedEvent(PRBool* aResult);
+  NS_IMETHOD    SetTrusted(PRBool aTrusted);
 
   NS_IMETHOD    IsHandled(PRBool* aHandled);
   NS_IMETHOD    SetHandled(PRBool aHandled);
@@ -245,6 +247,7 @@ protected:
   nsString*	mText;
   nsIPrivateTextRangeList*	mTextRange;
   PRPackedBool mEventIsInternal;
+  PRPackedBool mEventIsTrusted;
 
   //These are use for internal data for user created events
   PRInt16 mButton;
diff --git a/content/events/src/nsEventStateManager.cpp b/content/events/src/nsEventStateManager.cpp
index b578d460249..b79ea80531e 100644
--- a/content/events/src/nsEventStateManager.cpp
+++ b/content/events/src/nsEventStateManager.cpp
@@ -80,6 +80,7 @@
 
 #include "nsIServiceManager.h"
 #include "nsIPref.h"
+#include "nsIScriptSecurityManager.h"
 
 #include "nsIChromeEventHandler.h"
 #include "nsIFocusController.h"
@@ -3766,6 +3767,29 @@ nsEventStateManager::DispatchNewEvent(nsISupports* aTarget, nsIDOMEvent* aEvent,
     nsCOMPtr<nsIDOMEventTarget> eventTarget(do_QueryInterface(aTarget));
     privEvt->SetTarget(eventTarget);
 
+    //Key and mouse events have additional security to prevent event spoofing
+    nsEvent * internalEvent;
+    privEvt->GetInternalNSEvent(&internalEvent);
+    if (internalEvent && (internalEvent->eventStructType == NS_KEY_EVENT ||
+        internalEvent->eventStructType == NS_MOUSE_EVENT)) {
+      //Check security state to determine if dispatcher is trusted
+      nsCOMPtr<nsIScriptSecurityManager>
+      securityManager(do_GetService(NS_SCRIPTSECURITYMANAGER_CONTRACTID));
+      NS_ENSURE_TRUE(securityManager, NS_ERROR_FAILURE);
+
+      PRBool enabled;
+      nsresult res = securityManager->IsCapabilityEnabled("UniversalBrowserWrite", &enabled);
+      if (NS_SUCCEEDED(res) && enabled) {
+        privEvt->SetTrusted(PR_TRUE);
+      }
+      else {
+        privEvt->SetTrusted(PR_FALSE);
+      } 
+    }
+    else {
+      privEvt->SetTrusted(PR_TRUE);
+    }
+
     nsEvent* innerEvent;
     privEvt->GetInternalNSEvent(&innerEvent);
     if (innerEvent) {
diff --git a/content/xbl/src/nsXBLPrototypeHandler.cpp b/content/xbl/src/nsXBLPrototypeHandler.cpp
index d4f4aefd7f1..098161361f9 100644
--- a/content/xbl/src/nsXBLPrototypeHandler.cpp
+++ b/content/xbl/src/nsXBLPrototypeHandler.cpp
@@ -213,6 +213,17 @@ nsXBLPrototypeHandler::ExecuteHandler(nsIDOMEventReceiver* aReceiver,
   // See if our event receiver is a content node (and not us).
   PRBool isXULKey = (mType == NS_HANDLER_TYPE_XUL);
 
+  //XUL handlers shouldn't be triggered by non-trusted events.
+  if (isXULKey) {
+    nsCOMPtr<nsIPrivateDOMEvent> privateEvent = do_QueryInterface(aEvent);
+    if (privateEvent) {
+      PRBool trustedEvent;
+      privateEvent->IsTrustedEvent(&trustedEvent);
+      if (!trustedEvent)
+        return NS_OK;
+    }
+  }
+    
   PRBool isReceiverCommandElement = PR_FALSE;
   nsCOMPtr<nsIContent> content(do_QueryInterface(aReceiver));
   if (isXULKey && content && content.get() != mHandlerElement)
diff --git a/content/xbl/src/nsXBLWindowKeyHandler.cpp b/content/xbl/src/nsXBLWindowKeyHandler.cpp
index 0fd8b28cb2c..33b3aff8a75 100644
--- a/content/xbl/src/nsXBLWindowKeyHandler.cpp
+++ b/content/xbl/src/nsXBLWindowKeyHandler.cpp
@@ -46,6 +46,7 @@
 #include "nsIDOMNSUIEvent.h"
 #include "nsIDOMKeyEvent.h"
 #include "nsIDOMEventReceiver.h"
+#include "nsIPrivateDOMEvent.h"
 #include "nsXBLService.h"
 #include "nsIServiceManager.h"
 #include "nsHTMLAtoms.h"
@@ -145,6 +146,15 @@ nsXBLWindowKeyHandler::WalkHandlers(nsIDOMEvent* aKeyEvent, nsIAtom* aEventType)
   if (prevent)
     return NS_OK;
 
+  nsCOMPtr<nsIPrivateDOMEvent> privateEvent = do_QueryInterface(aKeyEvent);
+  if (privateEvent) {
+    //Don't process the event if it was not dispatched from a trusted source
+    PRBool trustedEvent;
+    privateEvent->IsTrustedEvent(&trustedEvent);
+    if (!trustedEvent)
+      return NS_OK;    
+  }
+
   // Make sure our event is really a key event
   nsCOMPtr<nsIDOMKeyEvent> keyEvent(do_QueryInterface(aKeyEvent));
   if (!keyEvent)
diff --git a/layout/xul/base/src/nsMenuListener.cpp b/layout/xul/base/src/nsMenuListener.cpp
index d8b4be36bc3..a065a3b174e 100644
--- a/layout/xul/base/src/nsMenuListener.cpp
+++ b/layout/xul/base/src/nsMenuListener.cpp
@@ -51,6 +51,7 @@
 #include "nsWidgetsCID.h"
 #include "nsCOMPtr.h"
 #include "nsIDOMKeyEvent.h"
+#include "nsIPrivateDOMEvent.h"
 #include "nsIPresContext.h"
 #include "nsIContent.h"
 #include "nsIDOMNode.h"
@@ -176,6 +177,17 @@ nsMenuListener::KeyPress(nsIDOMEvent* aKeyEvent)
       return NS_OK;       // don't consume event
   }
   
+  //handlers shouldn't be triggered by non-trusted events.
+  if (aKeyEvent) {
+    nsCOMPtr<nsIPrivateDOMEvent> privateEvent = do_QueryInterface(aKeyEvent);
+    if (privateEvent) {
+      PRBool trustedEvent;
+      privateEvent->IsTrustedEvent(&trustedEvent);
+      if (!trustedEvent)
+        return NS_OK;
+    }
+  }
+
   nsCOMPtr<nsIDOMKeyEvent> keyEvent = do_QueryInterface(aKeyEvent);
   PRUint32 theChar;
 	keyEvent->GetKeyCode(&theChar);