diff --git a/mozilla/layout/base/nsILayoutDebugger.h b/mozilla/layout/base/nsILayoutDebugger.h
index 51da819d6f1..75b4ba5b89c 100644
--- a/mozilla/layout/base/nsILayoutDebugger.h
+++ b/mozilla/layout/base/nsILayoutDebugger.h
@@ -41,6 +41,10 @@ public:
 
   NS_IMETHOD GetShowFrameBorders(PRBool* aResult) = 0;
 
+  NS_IMETHOD SetShowEventTargetFrameBorder(PRBool aEnable) = 0;
+
+  NS_IMETHOD GetShowEventTargetFrameBorder(PRBool* aResult) = 0;
+
   NS_IMETHOD GetContentSize(nsIDocument* aDocument,
                             PRInt32* aSizeInBytesResult) = 0;
 
diff --git a/mozilla/layout/base/nsLayoutDebugger.cpp b/mozilla/layout/base/nsLayoutDebugger.cpp
index cba7d560ada..bb2991f202e 100644
--- a/mozilla/layout/base/nsLayoutDebugger.cpp
+++ b/mozilla/layout/base/nsLayoutDebugger.cpp
@@ -37,6 +37,10 @@ public:
 
   NS_IMETHOD GetShowFrameBorders(PRBool* aResult);
 
+  NS_IMETHOD SetShowEventTargetFrameBorder(PRBool aEnable);
+
+  NS_IMETHOD GetShowEventTargetFrameBorder(PRBool* aResult);
+
   NS_IMETHOD GetContentSize(nsIDocument* aDocument,
                             PRInt32* aSizeInBytesResult);
 
@@ -87,6 +91,20 @@ nsLayoutDebugger::GetShowFrameBorders(PRBool* aResult)
   return NS_OK;
 }
 
+NS_IMETHODIMP
+nsLayoutDebugger::SetShowEventTargetFrameBorder(PRBool aEnable)
+{
+  nsIFrameDebug::ShowEventTargetFrameBorder(aEnable);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLayoutDebugger::GetShowEventTargetFrameBorder(PRBool* aResult)
+{
+  *aResult = nsIFrameDebug::GetShowEventTargetFrameBorder();
+  return NS_OK;
+}
+
 NS_IMETHODIMP
 nsLayoutDebugger::GetContentSize(nsIDocument* aDocument,
                                  PRInt32* aSizeInBytesResult)
diff --git a/mozilla/layout/base/nsPresShell.cpp b/mozilla/layout/base/nsPresShell.cpp
index e8bcef5ac10..70447a02f2f 100644
--- a/mozilla/layout/base/nsPresShell.cpp
+++ b/mozilla/layout/base/nsPresShell.cpp
@@ -477,6 +477,10 @@ protected:
   nsIFrame* mCurrentEventFrame;
   nsIContent* mCurrentEventContent;
   nsVoidArray mCurrentEventFrameStack;
+#ifdef NS_DEBUG
+  nsRect mCurrentTargetRect;
+  nsIView* mCurrentTargetView;
+#endif
   
   nsCOMPtr<nsIFrameSelection>   mSelection;
   nsCOMPtr<nsICaret>            mCaret;
@@ -618,6 +622,9 @@ PresShell::PresShell()
   mCurrentEventContent = nsnull;
   mCurrentEventFrame = nsnull;
   EnableScrolling();
+#ifdef NS_DEBUG
+  mCurrentTargetView = nsnull;
+#endif
   mPendingReflowEvent = PR_FALSE;  
   mDocumentIsLoading = PR_TRUE;
   mBatchReflows = PR_FALSE;
@@ -2734,6 +2741,11 @@ PresShell::Paint(nsIView              *aView,
       aRenderingContext.SetColor(NS_RGB(0,0,255));
       aRenderingContext.DrawRect(0, 0, r.width, r.height);
     }
+    // Draw a border around the current event target
+    if ((nsIFrameDebug::GetShowEventTargetFrameBorder()) && (aView == mCurrentTargetView)) {
+      aRenderingContext.SetColor(NS_RGB(128,0,128));
+      aRenderingContext.DrawRect(mCurrentTargetRect.x, mCurrentTargetRect.y, mCurrentTargetRect.width, mCurrentTargetRect.height);
+    }
 #endif
   }
 
@@ -2856,6 +2868,32 @@ PresShell::HandleEvent(nsIView         *aView,
       NS_RELEASE(manager);
       NS_IF_RELEASE(focusContent);
     }
+#ifdef NS_DEBUG
+    if ((nsIFrameDebug::GetShowEventTargetFrameBorder()) && (GetCurrentEventFrame())) {
+      nsIView *oldView = mCurrentTargetView;
+      nsPoint offset(0,0);
+      nsRect oldTargetRect(mCurrentTargetRect);
+      mCurrentEventFrame->GetRect(mCurrentTargetRect);
+      mCurrentEventFrame->GetView(mPresContext, &mCurrentTargetView);
+      if ( ! mCurrentTargetView ) {
+        mCurrentEventFrame->GetOffsetFromView(mPresContext, offset, &mCurrentTargetView);
+      }
+      if (mCurrentTargetView) {
+        mCurrentTargetRect.x = offset.x;
+        mCurrentTargetRect.y = offset.y;
+        // use aView or mCurrentTargetView??
+        if ( (mCurrentTargetRect != oldTargetRect) || (mCurrentTargetView != oldView)) {
+          nsIViewManager *vm;
+          if ((NS_OK == GetViewManager(&vm)) && vm) {
+            vm->UpdateView(mCurrentTargetView,mCurrentTargetRect,0);
+            if (oldView)
+              vm->UpdateView(oldView,oldTargetRect,0);
+            NS_IF_RELEASE(vm);
+          }
+        }
+      }
+    }
+#endif
     PopCurrentEventFrame();
   }
   else {
diff --git a/mozilla/layout/base/public/nsIFrameDebug.h b/mozilla/layout/base/public/nsIFrameDebug.h
index 7dd5cf034d6..29eaacbee54 100644
--- a/mozilla/layout/base/public/nsIFrameDebug.h
+++ b/mozilla/layout/base/public/nsIFrameDebug.h
@@ -115,6 +115,10 @@ public:
   static NS_LAYOUT void ShowFrameBorders(PRBool aEnable);
   static NS_LAYOUT PRBool GetShowFrameBorders();
 
+  // Show frame border of event target
+  static NS_LAYOUT void ShowEventTargetFrameBorder(PRBool aEnable);
+  static NS_LAYOUT PRBool GetShowEventTargetFrameBorder();
+
 private:
   NS_IMETHOD_(nsrefcnt) AddRef(void) = 0;
   NS_IMETHOD_(nsrefcnt) Release(void) = 0;
diff --git a/mozilla/layout/base/public/nsILayoutDebugger.h b/mozilla/layout/base/public/nsILayoutDebugger.h
index 51da819d6f1..75b4ba5b89c 100644
--- a/mozilla/layout/base/public/nsILayoutDebugger.h
+++ b/mozilla/layout/base/public/nsILayoutDebugger.h
@@ -41,6 +41,10 @@ public:
 
   NS_IMETHOD GetShowFrameBorders(PRBool* aResult) = 0;
 
+  NS_IMETHOD SetShowEventTargetFrameBorder(PRBool aEnable) = 0;
+
+  NS_IMETHOD GetShowEventTargetFrameBorder(PRBool* aResult) = 0;
+
   NS_IMETHOD GetContentSize(nsIDocument* aDocument,
                             PRInt32* aSizeInBytesResult) = 0;
 
diff --git a/mozilla/layout/base/src/nsLayoutDebugger.cpp b/mozilla/layout/base/src/nsLayoutDebugger.cpp
index cba7d560ada..bb2991f202e 100644
--- a/mozilla/layout/base/src/nsLayoutDebugger.cpp
+++ b/mozilla/layout/base/src/nsLayoutDebugger.cpp
@@ -37,6 +37,10 @@ public:
 
   NS_IMETHOD GetShowFrameBorders(PRBool* aResult);
 
+  NS_IMETHOD SetShowEventTargetFrameBorder(PRBool aEnable);
+
+  NS_IMETHOD GetShowEventTargetFrameBorder(PRBool* aResult);
+
   NS_IMETHOD GetContentSize(nsIDocument* aDocument,
                             PRInt32* aSizeInBytesResult);
 
@@ -87,6 +91,20 @@ nsLayoutDebugger::GetShowFrameBorders(PRBool* aResult)
   return NS_OK;
 }
 
+NS_IMETHODIMP
+nsLayoutDebugger::SetShowEventTargetFrameBorder(PRBool aEnable)
+{
+  nsIFrameDebug::ShowEventTargetFrameBorder(aEnable);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLayoutDebugger::GetShowEventTargetFrameBorder(PRBool* aResult)
+{
+  *aResult = nsIFrameDebug::GetShowEventTargetFrameBorder();
+  return NS_OK;
+}
+
 NS_IMETHODIMP
 nsLayoutDebugger::GetContentSize(nsIDocument* aDocument,
                                  PRInt32* aSizeInBytesResult)
diff --git a/mozilla/layout/generic/nsFrame.cpp b/mozilla/layout/generic/nsFrame.cpp
index a068cd83229..dda1e3fb000 100644
--- a/mozilla/layout/generic/nsFrame.cpp
+++ b/mozilla/layout/generic/nsFrame.cpp
@@ -107,6 +107,18 @@ NS_LAYOUT PRBool nsIFrameDebug::GetShowFrameBorders()
   return gShowFrameBorders;
 }
 
+static PRBool gShowEventTargetFrameBorder = PR_FALSE;
+
+NS_LAYOUT void nsIFrameDebug::ShowEventTargetFrameBorder(PRBool aEnable)
+{
+  gShowEventTargetFrameBorder = aEnable;
+}
+
+NS_LAYOUT PRBool nsIFrameDebug::GetShowEventTargetFrameBorder()
+{
+  return gShowEventTargetFrameBorder;
+}
+
 /**
  * Note: the log module is created during library initialization which
  * means that you cannot perform logging before then.
diff --git a/mozilla/layout/generic/nsIFrameDebug.h b/mozilla/layout/generic/nsIFrameDebug.h
index 7dd5cf034d6..29eaacbee54 100644
--- a/mozilla/layout/generic/nsIFrameDebug.h
+++ b/mozilla/layout/generic/nsIFrameDebug.h
@@ -115,6 +115,10 @@ public:
   static NS_LAYOUT void ShowFrameBorders(PRBool aEnable);
   static NS_LAYOUT PRBool GetShowFrameBorders();
 
+  // Show frame border of event target
+  static NS_LAYOUT void ShowEventTargetFrameBorder(PRBool aEnable);
+  static NS_LAYOUT PRBool GetShowEventTargetFrameBorder();
+
 private:
   NS_IMETHOD_(nsrefcnt) AddRef(void) = 0;
   NS_IMETHOD_(nsrefcnt) Release(void) = 0;
diff --git a/mozilla/layout/html/base/src/nsFrame.cpp b/mozilla/layout/html/base/src/nsFrame.cpp
index a068cd83229..dda1e3fb000 100644
--- a/mozilla/layout/html/base/src/nsFrame.cpp
+++ b/mozilla/layout/html/base/src/nsFrame.cpp
@@ -107,6 +107,18 @@ NS_LAYOUT PRBool nsIFrameDebug::GetShowFrameBorders()
   return gShowFrameBorders;
 }
 
+static PRBool gShowEventTargetFrameBorder = PR_FALSE;
+
+NS_LAYOUT void nsIFrameDebug::ShowEventTargetFrameBorder(PRBool aEnable)
+{
+  gShowEventTargetFrameBorder = aEnable;
+}
+
+NS_LAYOUT PRBool nsIFrameDebug::GetShowEventTargetFrameBorder()
+{
+  return gShowEventTargetFrameBorder;
+}
+
 /**
  * Note: the log module is created during library initialization which
  * means that you cannot perform logging before then.
diff --git a/mozilla/layout/html/base/src/nsPresShell.cpp b/mozilla/layout/html/base/src/nsPresShell.cpp
index e8bcef5ac10..70447a02f2f 100644
--- a/mozilla/layout/html/base/src/nsPresShell.cpp
+++ b/mozilla/layout/html/base/src/nsPresShell.cpp
@@ -477,6 +477,10 @@ protected:
   nsIFrame* mCurrentEventFrame;
   nsIContent* mCurrentEventContent;
   nsVoidArray mCurrentEventFrameStack;
+#ifdef NS_DEBUG
+  nsRect mCurrentTargetRect;
+  nsIView* mCurrentTargetView;
+#endif
   
   nsCOMPtr<nsIFrameSelection>   mSelection;
   nsCOMPtr<nsICaret>            mCaret;
@@ -618,6 +622,9 @@ PresShell::PresShell()
   mCurrentEventContent = nsnull;
   mCurrentEventFrame = nsnull;
   EnableScrolling();
+#ifdef NS_DEBUG
+  mCurrentTargetView = nsnull;
+#endif
   mPendingReflowEvent = PR_FALSE;  
   mDocumentIsLoading = PR_TRUE;
   mBatchReflows = PR_FALSE;
@@ -2734,6 +2741,11 @@ PresShell::Paint(nsIView              *aView,
       aRenderingContext.SetColor(NS_RGB(0,0,255));
       aRenderingContext.DrawRect(0, 0, r.width, r.height);
     }
+    // Draw a border around the current event target
+    if ((nsIFrameDebug::GetShowEventTargetFrameBorder()) && (aView == mCurrentTargetView)) {
+      aRenderingContext.SetColor(NS_RGB(128,0,128));
+      aRenderingContext.DrawRect(mCurrentTargetRect.x, mCurrentTargetRect.y, mCurrentTargetRect.width, mCurrentTargetRect.height);
+    }
 #endif
   }
 
@@ -2856,6 +2868,32 @@ PresShell::HandleEvent(nsIView         *aView,
       NS_RELEASE(manager);
       NS_IF_RELEASE(focusContent);
     }
+#ifdef NS_DEBUG
+    if ((nsIFrameDebug::GetShowEventTargetFrameBorder()) && (GetCurrentEventFrame())) {
+      nsIView *oldView = mCurrentTargetView;
+      nsPoint offset(0,0);
+      nsRect oldTargetRect(mCurrentTargetRect);
+      mCurrentEventFrame->GetRect(mCurrentTargetRect);
+      mCurrentEventFrame->GetView(mPresContext, &mCurrentTargetView);
+      if ( ! mCurrentTargetView ) {
+        mCurrentEventFrame->GetOffsetFromView(mPresContext, offset, &mCurrentTargetView);
+      }
+      if (mCurrentTargetView) {
+        mCurrentTargetRect.x = offset.x;
+        mCurrentTargetRect.y = offset.y;
+        // use aView or mCurrentTargetView??
+        if ( (mCurrentTargetRect != oldTargetRect) || (mCurrentTargetView != oldView)) {
+          nsIViewManager *vm;
+          if ((NS_OK == GetViewManager(&vm)) && vm) {
+            vm->UpdateView(mCurrentTargetView,mCurrentTargetRect,0);
+            if (oldView)
+              vm->UpdateView(oldView,oldTargetRect,0);
+            NS_IF_RELEASE(vm);
+          }
+        }
+      }
+    }
+#endif
     PopCurrentEventFrame();
   }
   else {