--- a/editor/libeditor/HTMLEditor.h
+++ b/editor/libeditor/HTMLEditor.h
@@ -12,17 +12,16 @@
 #include "mozilla/StyleSheet.h"
 #include "mozilla/TextEditor.h"
 #include "mozilla/UniquePtr.h"
 #include "mozilla/dom/Element.h"
 #include "mozilla/dom/File.h"
 
 #include "nsAttrName.h"
 #include "nsCOMPtr.h"
-#include "nsIContentFilter.h"
 #include "nsICSSLoaderObserver.h"
 #include "nsIDocumentObserver.h"
 #include "nsIDOMElement.h"
 #include "nsIDOMEventListener.h"
 #include "nsIEditorMailSupport.h"
 #include "nsIEditorStyleSheets.h"
 #include "nsIEditorUtils.h"
 #include "nsIEditRules.h"
@@ -644,27 +643,16 @@ protected:
                                           int32_t aIndex,
                                           nsIDOMDocument* aSourceDoc,
                                           nsIDOMNode* aDestinationNode,
                                           int32_t aDestOffset,
                                           bool aDoDeleteSelection) override;
   bool HavePrivateHTMLFlavor(nsIClipboard* clipboard );
   nsresult ParseCFHTML(nsCString& aCfhtml, char16_t** aStuffToPaste,
                        char16_t** aCfcontext);
-  nsresult DoContentFilterCallback(const nsAString& aFlavor,
-                                   nsIDOMDocument* aSourceDoc,
-                                   bool aWillDeleteSelection,
-                                   nsIDOMNode** aFragmentAsNode,
-                                   nsIDOMNode** aFragStartNode,
-                                   int32_t* aFragStartOffset,
-                                   nsIDOMNode** aFragEndNode,
-                                   int32_t* aFragEndOffset,
-                                   nsIDOMNode** aTargetNode,
-                                   int32_t* aTargetOffset,
-                                   bool* aDoContinue);
 
   bool IsInLink(nsIDOMNode* aNode, nsCOMPtr<nsIDOMNode>* outLink = nullptr);
   nsresult StripFormattingNodes(nsIContent& aNode, bool aOnlyList = false);
   nsresult CreateDOMFragmentFromPaste(const nsAString& aInputString,
                                       const nsAString& aContextStr,
                                       const nsAString& aInfoStr,
                                       nsCOMPtr<nsIDOMNode>* outFragNode,
                                       nsCOMPtr<nsIDOMNode>* outStartNode,
@@ -919,18 +907,16 @@ protected:
    *                    AutoSelectionSetterAfterTableEdit stack-based object to
    *                    insure we reset the caret in a table-editing method.
    */
   void SetSelectionAfterTableEdit(nsIDOMElement* aTable,
                                   int32_t aRow, int32_t aCol,
                                   int32_t aDirection, bool aSelected);
 
 protected:
-  nsTArray<OwningNonNull<nsIContentFilter>> mContentFilters;
-
   RefPtr<TypeInState> mTypeInState;
 
   bool mCRInParagraphCreatesParagraph;
 
   bool mCSSAware;
   UniquePtr<CSSEditUtils> mCSSEditUtils;
 
   // Used by GetFirstSelectedCell and GetNextSelectedCell

--- a/editor/libeditor/HTMLEditorDataTransfer.cpp
+++ b/editor/libeditor/HTMLEditorDataTransfer.cpp
@@ -30,17 +30,16 @@
 #include "nsIScriptError.h"
 #include "nsContentUtils.h"
 #include "nsDebug.h"
 #include "nsDependentSubstring.h"
 #include "nsError.h"
 #include "nsGkAtoms.h"
 #include "nsIClipboard.h"
 #include "nsIContent.h"
-#include "nsIContentFilter.h"
 #include "nsIDOMComment.h"
 #include "nsIDOMDocument.h"
 #include "nsIDOMDocumentFragment.h"
 #include "nsIDOMElement.h"
 #include "nsIDOMHTMLInputElement.h"
 #include "nsIDOMNode.h"
 #include "nsIDocument.h"
 #include "nsIEditRules.h"
@@ -221,30 +220,16 @@ HTMLEditor::DoInsertHTMLWithContext(cons
     if (!targetNode || !IsEditable(targetNode)) {
       return NS_ERROR_FAILURE;
     }
   } else {
     targetNode = aDestNode;
     targetOffset = aDestOffset;
   }
 
-  bool doContinue = true;
-
-  rv = DoContentFilterCallback(aFlavor, aSourceDoc, aDeleteSelection,
-                               (nsIDOMNode **)address_of(fragmentAsNode),
-                               (nsIDOMNode **)address_of(streamStartParent),
-                               &streamStartOffset,
-                               (nsIDOMNode **)address_of(streamEndParent),
-                               &streamEndOffset,
-                               (nsIDOMNode **)address_of(targetNode),
-                               &targetOffset, &doContinue);
-
-  NS_ENSURE_SUCCESS(rv, rv);
-  NS_ENSURE_TRUE(doContinue, NS_OK);
-
   // if we have a destination / target node, we want to insert there
   // rather than in place of the selection
   // ignore aDeleteSelection here if no aDestNode since deletion will
   // also occur later; this block is intended to cover the various
   // scenarios where we are dropping in an editor (and may want to delete
   // the selection before collapsing the selection in the new destination)
   if (aDestNode) {
     if (aDeleteSelection) {
@@ -664,68 +649,16 @@ HTMLEditor::DoInsertHTMLWithContext(cons
         }
       }
     }
   }
 
   return rules->DidDoAction(selection, &ruleInfo, rv);
 }
 
-NS_IMETHODIMP
-HTMLEditor::AddInsertionListener(nsIContentFilter* aListener)
-{
-  NS_ENSURE_TRUE(aListener, NS_ERROR_NULL_POINTER);
-
-  // don't let a listener be added more than once
-  if (!mContentFilters.Contains(aListener)) {
-    mContentFilters.AppendElement(*aListener);
-  }
-
-  return NS_OK;
-}
-
-NS_IMETHODIMP
-HTMLEditor::RemoveInsertionListener(nsIContentFilter* aListener)
-{
-  NS_ENSURE_TRUE(aListener, NS_ERROR_FAILURE);
-
-  mContentFilters.RemoveElement(aListener);
-
-  return NS_OK;
-}
-
-nsresult
-HTMLEditor::DoContentFilterCallback(const nsAString& aFlavor,
-                                    nsIDOMDocument* sourceDoc,
-                                    bool aWillDeleteSelection,
-                                    nsIDOMNode** aFragmentAsNode,
-                                    nsIDOMNode** aFragStartNode,
-                                    int32_t* aFragStartOffset,
-                                    nsIDOMNode** aFragEndNode,
-                                    int32_t* aFragEndOffset,
-                                    nsIDOMNode** aTargetNode,
-                                    int32_t* aTargetOffset,
-                                    bool* aDoContinue)
-{
-  *aDoContinue = true;
-
-  for (auto& listener : mContentFilters) {
-    if (!*aDoContinue) {
-      break;
-    }
-    listener->NotifyOfInsertion(aFlavor, nullptr, sourceDoc,
-                                aWillDeleteSelection, aFragmentAsNode,
-                                aFragStartNode, aFragStartOffset,
-                                aFragEndNode, aFragEndOffset, aTargetNode,
-                                aTargetOffset, aDoContinue);
-  }
-
-  return NS_OK;
-}
-
 bool
 HTMLEditor::IsInLink(nsIDOMNode* aNode,
                      nsCOMPtr<nsIDOMNode>* outLink)
 {
   NS_ENSURE_TRUE(aNode, false);
   if (outLink) {
     *outLink = nullptr;
   }

--- a/editor/moz.build
+++ b/editor/moz.build
@@ -7,17 +7,16 @@
 DIRS += [
     'txtsvc',
     'libeditor',
     'txmgr',
     'composer',
 ]
 
 XPIDL_SOURCES += [
-    'nsIContentFilter.idl',
     'nsIDocumentStateListener.idl',
     'nsIEditActionListener.idl',
     'nsIEditor.idl',
     'nsIEditorMailSupport.idl',
     'nsIEditorObserver.idl',
     'nsIEditorSpellCheck.idl',
     'nsIEditorStyleSheets.idl',
     'nsIEditorUtils.idl',

deleted file mode 100644
--- a/editor/nsIContentFilter.idl
+++ /dev/null
@@ -1,85 +0,0 @@
-/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-#include "nsISupports.idl"
-#include "domstubs.idl"
-
-interface nsIURL;
-
-[scriptable, uuid(c18c49a8-62f0-4045-9884-4aa91e388f14)]
-interface nsIContentFilter : nsISupports
-{
-  /**
-   * This notification occurs in an editor during these events:
-   *    * open of document (once rendered in window but before editable)
-   *    * paste from clipboard
-   *    * drop from mouse
-   *    * insertion of html (such as with "cmd_insertHTML")
-   * It provides a hook so the above actions can be canceled or the data
-   * can be modified (using standard DOM APIs) or left untouched.  The data
-   * that results (if any) from all filter callbacks is what will be used
-   * for transaction purposes (undo/redo) except for the open event.
-   *
-   * The willDeleteSelection parameter is offered for filters who want to
-   * handle the insertion themselves and need to handle drag/drop correctly.
-   * The flag is true when the editor intends to delete the selection.
-   *
-   * Callers who want to cancel all insertion can simply set
-   * continueWithInsertion to PR_FALSE and return.
-   * Note: If cancellation occurs during the "open" event, the editor will
-   * still be available but will be empty.
-   *
-   * Callers who want to allow insertion of the data with no changes
-   * can simply set continueWithInsertion to PR_TRUE and return.
-   *
-   * Callers who want to modify the content (docFragment) being inserted are
-   * responsible for updating contentStartNode, contentStartOffset,
-   * contentEndNode, and contentEndOffset (if necessary).
-   * Callers are responsible for freeing and addref'ing if they want to
-   * completely replace any of the DOM nodes passed in.
-   *
-   * The location where insertion will occur should be considered an
-   * approximation since the editor may need to adjust it if it deletes
-   * the selection as part of the event and later determines that insertion
-   * point is an empty container which should also be removed (or in other
-   * scenarios such as -moz-user-select:none).
-   *
-   * In some scenarios the selection will be deleted.  If callers choose
-   * to adjust the insertion point, they should be careful that the insertion
-   * point is not in the current selection.
-   *
-   * The contentStartNode and contentEndNode are not necessarily
-   * immediate children of the docFragment.  Any nodes outside of the range
-   * set by contentStartNode and contentEndNode are for context from the
-   * source document.
-   *
-   * @param mimeType          the mimetype used for retrieving data
-   * @param contentSourceURL  location where docFragment came from
-   * @param sourceDocument      document where content came from (can be null)
-   * @param willDeleteSelection tells hook if selection will/should be deleted
-   * @param docFragment         fragment of node to be inserted
-   * @param contentStartNode    node under which content to be inserted begins
-   * @param contentStartOffset  start offset within contentStartNode
-   * @param contentEndNode      node under which content to be inserted ends
-   * @param contentEndOffset    ending offset withing contentEndNode
-   * @param insertionPointNode     location where insertion will occur
-   * @param insertionPointOffset   offset within node where insertion occurs
-   * @param continueWithInsertion  flag to cancel insertion (if desired)
-   */
-
-  void notifyOfInsertion(in AString mimeType,
-                         in nsIURL contentSourceURL,
-                         in nsIDOMDocument sourceDocument,
-                         in boolean willDeleteSelection,
-                         inout nsIDOMNode docFragment,
-                         inout nsIDOMNode contentStartNode,
-                         inout long contentStartOffset,
-                         inout nsIDOMNode contentEndNode,
-                         inout long contentEndOffset,
-                         inout nsIDOMNode insertionPointNode,
-                         inout long insertionPointOffset,
-                         out boolean continueWithInsertion);
-
-};

--- a/editor/nsIHTMLEditor.idl
+++ b/editor/nsIHTMLEditor.idl
@@ -4,17 +4,16 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "nsISupports.idl"
 #include "domstubs.idl"
 
 interface nsIContent;
 interface nsIArray;
 interface nsISelection;
-interface nsIContentFilter;
 
 %{C++
 namespace mozilla {
 namespace dom {
 class Element;
 }
 }
 %}
@@ -450,28 +449,16 @@ interface nsIHTMLEditor : nsISupports
    * A boolean which is true is the HTMLEditor has been instantiated
    * with CSS knowledge and if the CSS pref is currently checked
    *
    * @return    true if CSS handled and enabled
    */
   attribute boolean isCSSEnabled;
 
   /**
-   * Add listener for insertion override
-   * @param inFilter  function which callers want called during insertion
-   */
-  void addInsertionListener(in nsIContentFilter inFilter);
-
-  /**
-   * Remove listener for insertion override
-   * @param inFilter  function which callers do not want called during insertion
-   */
-  void removeInsertionListener(in nsIContentFilter inFilter);
-
-  /**
    * returns the deepest container of the selection
    * @return a DOM Element
    */
   nsIDOMElement getSelectionContainer();
 
   /**
    * Checks if the anonymous nodes created by the HTML editor have to be
    * refreshed or hidden depending on a possible new state of the selection