diff --git a/editor/libeditor/base/nsEditRules.h b/editor/libeditor/base/nsEditRules.h
index 472008b06b16..8965f8f04c0c 100644
--- a/editor/libeditor/base/nsEditRules.h
+++ b/editor/libeditor/base/nsEditRules.h
@@ -38,10 +38,10 @@
 #ifndef nsEditRules_h__
 #define nsEditRules_h__
 
+// 783223c9-153a-4e01-8422-39a3afe469da
 #define NS_IEDITRULES_IID \
-{ /* a6cf911d-15b3-11d2-932e-00805f8add32 */ \
-0xa6cf911d, 0x15b3, 0x11d2, \
-{0x93, 0x2e, 0x00, 0x80, 0x5f, 0x8a, 0xdd, 0x32} }
+{ 0x783223c9, 0x153a, 0x4e01, \
+  { 0x84, 0x22, 0x39, 0xa3, 0xaf, 0xe4, 0x69, 0xda } }
 
 class nsPlaintextEditor;
 class nsISelection;
@@ -73,6 +73,7 @@ public:
 //NOTE: Use   NS_DECL_ISUPPORTS_INHERITED in any class inherited from nsIEditRules
 
   NS_IMETHOD Init(nsPlaintextEditor *aEditor, PRUint32 aFlags)=0;
+  NS_IMETHOD DetachEditor()=0;
   NS_IMETHOD BeforeEdit(PRInt32 action, nsIEditor::EDirection aDirection)=0;
   NS_IMETHOD AfterEdit(PRInt32 action, nsIEditor::EDirection aDirection)=0;
   NS_IMETHOD WillDoAction(nsISelection *aSelection, nsRulesInfo *aInfo, PRBool *aCancel, PRBool *aHandled)=0;
diff --git a/editor/libeditor/html/nsHTMLEditRules.cpp b/editor/libeditor/html/nsHTMLEditRules.cpp
index 83bf7a63d54d..947e71c8ed8b 100644
--- a/editor/libeditor/html/nsHTMLEditRules.cpp
+++ b/editor/libeditor/html/nsHTMLEditRules.cpp
@@ -225,11 +225,12 @@ mDocChangeRange(nsnull)
 nsHTMLEditRules::~nsHTMLEditRules()
 {
   // remove ourselves as a listener to edit actions
-  // In the normal case, we have already been removed by 
-  // ~nsHTMLEditor, in which case we will get an error here
+  // In some cases, we have already been removed by 
+  // ~nsHTMLEditor, in which case we will get a null pointer here
   // which we ignore.  But this allows us to add the ability to
   // switch rule sets on the fly if we want.
-  mHTMLEditor->RemoveEditActionListener(this);
+  if (mHTMLEditor)
+    mHTMLEditor->RemoveEditActionListener(this);
 }
 
 /********************************************************
@@ -302,6 +303,12 @@ nsHTMLEditRules::Init(nsPlaintextEditor *aEditor, PRUint32 aFlags)
   return res;
 }
 
+NS_IMETHODIMP
+nsHTMLEditRules::DetachEditor()
+{
+  mHTMLEditor = nsnull;
+  return nsTextEditRules::DetachEditor();
+}
 
 NS_IMETHODIMP
 nsHTMLEditRules::BeforeEdit(PRInt32 action, nsIEditor::EDirection aDirection)
diff --git a/editor/libeditor/html/nsHTMLEditRules.h b/editor/libeditor/html/nsHTMLEditRules.h
index 818cb28ac8b4..2c5adce16fa4 100644
--- a/editor/libeditor/html/nsHTMLEditRules.h
+++ b/editor/libeditor/html/nsHTMLEditRules.h
@@ -87,6 +87,7 @@ public:
 
   // nsIEditRules methods
   NS_IMETHOD Init(nsPlaintextEditor *aEditor, PRUint32 aFlags);
+  NS_IMETHOD DetachEditor();
   NS_IMETHOD BeforeEdit(PRInt32 action, nsIEditor::EDirection aDirection);
   NS_IMETHOD AfterEdit(PRInt32 action, nsIEditor::EDirection aDirection);
   NS_IMETHOD WillDoAction(nsISelection *aSelection, nsRulesInfo *aInfo, PRBool *aCancel, PRBool *aHandled);
diff --git a/editor/libeditor/text/nsPlaintextEditor.cpp b/editor/libeditor/text/nsPlaintextEditor.cpp
index 7270afad9e60..84eb1dbbbf41 100644
--- a/editor/libeditor/text/nsPlaintextEditor.cpp
+++ b/editor/libeditor/text/nsPlaintextEditor.cpp
@@ -115,6 +115,9 @@ nsPlaintextEditor::~nsPlaintextEditor()
   // Remove event listeners. Note that if we had an HTML editor,
   //  it installed its own instead of these
   RemoveEventListeners();
+
+  if (mRules)
+    mRules->DetachEditor();
 }
 
 NS_IMPL_ADDREF_INHERITED(nsPlaintextEditor, nsEditor)
diff --git a/editor/libeditor/text/nsTextEditRules.cpp b/editor/libeditor/text/nsTextEditRules.cpp
index 54fdc347f26f..15f6f8f05359 100644
--- a/editor/libeditor/text/nsTextEditRules.cpp
+++ b/editor/libeditor/text/nsTextEditRules.cpp
@@ -182,6 +182,13 @@ nsTextEditRules::Init(nsPlaintextEditor *aEditor, PRUint32 aFlags)
   return res;
 }
 
+NS_IMETHODIMP
+nsTextEditRules::DetachEditor()
+{
+  mEditor = nsnull;
+  return NS_OK;
+}
+
 NS_IMETHODIMP
 nsTextEditRules::GetFlags(PRUint32 *aFlags)
 {
diff --git a/editor/libeditor/text/nsTextEditRules.h b/editor/libeditor/text/nsTextEditRules.h
index 7e467d2e928f..a4a16de61332 100644
--- a/editor/libeditor/text/nsTextEditRules.h
+++ b/editor/libeditor/text/nsTextEditRules.h
@@ -66,6 +66,7 @@ public:
 
   // nsIEditRules methods
   NS_IMETHOD Init(nsPlaintextEditor *aEditor, PRUint32 aFlags);
+  NS_IMETHOD DetachEditor();
   NS_IMETHOD BeforeEdit(PRInt32 action, nsIEditor::EDirection aDirection);
   NS_IMETHOD AfterEdit(PRInt32 action, nsIEditor::EDirection aDirection);
   NS_IMETHOD WillDoAction(nsISelection *aSelection, nsRulesInfo *aInfo, PRBool *aCancel, PRBool *aHandled);