diff --git a/dom/base/StyleSheetList.cpp b/dom/base/StyleSheetList.cpp
index e1815c96f003..bb49ec100571 100644
--- a/dom/base/StyleSheetList.cpp
+++ b/dom/base/StyleSheetList.cpp
@@ -28,7 +28,7 @@ JSObject* StyleSheetList::WrapObject(JSContext* aCx,
   return StyleSheetList_Binding::Wrap(aCx, this, aGivenProto);
 }
 
-void StyleSheetList::NodeWillBeDestroyed(nsINode* aNode) {
+void StyleSheetList::NodeWillBeDestroyed(const nsINode* aNode) {
   mDocumentOrShadowRoot = nullptr;
 }
 
diff --git a/dom/base/nsContentList.cpp b/dom/base/nsContentList.cpp
index 22aab8d55171..4bada9122818 100644
--- a/dom/base/nsContentList.cpp
+++ b/dom/base/nsContentList.cpp
@@ -590,7 +590,7 @@ int32_t nsContentList::IndexOf(nsIContent* aContent) {
   return IndexOf(aContent, true);
 }
 
-void nsContentList::NodeWillBeDestroyed(nsINode* aNode) {
+void nsContentList::NodeWillBeDestroyed(const nsINode* aNode) {
   // We shouldn't do anything useful from now on
 
   RemoveFromCaches();
diff --git a/dom/base/nsDOMMutationObserver.cpp b/dom/base/nsDOMMutationObserver.cpp
index a97b4bca981f..9b35ffeae4ec 100644
--- a/dom/base/nsDOMMutationObserver.cpp
+++ b/dom/base/nsDOMMutationObserver.cpp
@@ -374,7 +374,7 @@ void nsMutationReceiver::ContentRemoved(nsIContent* aChild,
   Observer()->ScheduleForRun();
 }
 
-void nsMutationReceiver::NodeWillBeDestroyed(nsINode* aNode) {
+void nsMutationReceiver::NodeWillBeDestroyed(const nsINode* aNode) {
   NS_ASSERTION(!mParent, "Shouldn't have mParent here!");
   Disconnect(true);
 }
diff --git a/dom/base/nsIMutationObserver.h b/dom/base/nsIMutationObserver.h
index 6e25d11eee72..abc3ffdba029 100644
--- a/dom/base/nsIMutationObserver.h
+++ b/dom/base/nsIMutationObserver.h
@@ -288,7 +288,7 @@ class nsIMutationObserver
    *       the observer.  The observer is responsible for making sure it
    *       stays alive for the duration of the call as needed.
    */
-  virtual void NodeWillBeDestroyed(nsINode* aNode) = 0;
+  virtual void NodeWillBeDestroyed(const nsINode* aNode) = 0;
 
   /**
    * Notification that the node's parent chain has changed. This
@@ -345,7 +345,7 @@ NS_DEFINE_STATIC_IID_ACCESSOR(nsIMutationObserver, NS_IMUTATION_OBSERVER_IID)
                               nsIContent* aPreviousSibling) override;
 
 #define NS_DECL_NSIMUTATIONOBSERVER_NODEWILLBEDESTROYED \
-  virtual void NodeWillBeDestroyed(nsINode* aNode) override;
+  virtual void NodeWillBeDestroyed(const nsINode* aNode) override;
 
 #define NS_DECL_NSIMUTATIONOBSERVER_PARENTCHAINCHANGED \
   virtual void ParentChainChanged(nsIContent* aContent) override;
@@ -363,7 +363,7 @@ NS_DEFINE_STATIC_IID_ACCESSOR(nsIMutationObserver, NS_IMUTATION_OBSERVER_IID)
   NS_DECL_NSIMUTATIONOBSERVER_PARENTCHAINCHANGED
 
 #define NS_IMPL_NSIMUTATIONOBSERVER_CORE_STUB(_class) \
-  void _class::NodeWillBeDestroyed(nsINode* aNode) {}
+  void _class::NodeWillBeDestroyed(const nsINode* aNode) {}
 
 #define NS_IMPL_NSIMUTATIONOBSERVER_CONTENT(_class)                          \
   void _class::CharacterDataWillChange(                                      \
diff --git a/dom/base/nsStubMutationObserver.cpp b/dom/base/nsStubMutationObserver.cpp
index a7d017474a70..e0ea4941d65c 100644
--- a/dom/base/nsStubMutationObserver.cpp
+++ b/dom/base/nsStubMutationObserver.cpp
@@ -100,12 +100,11 @@ class MutationObserverWrapper final : public nsIMutationObserver {
     mOwner->ContentRemoved(aChild, aPreviousSibling);
   }
 
-  void NodeWillBeDestroyed(nsINode* aNode) override {
+  void NodeWillBeDestroyed(const nsINode* aNode) override {
     MOZ_ASSERT(mOwner);
-    AddRefWrapper();
     RefPtr<nsMultiMutationObserver> owner = mOwner;
     owner->NodeWillBeDestroyed(aNode);
-    owner->RemoveMutationObserverFromNode(aNode);
+    owner->mWrapperForNode.Remove(const_cast<nsINode*>(aNode));
     mOwner = nullptr;
     ReleaseWrapper();
   }
diff --git a/dom/base/nsTextNode.cpp b/dom/base/nsTextNode.cpp
index fd56b04c57d6..b92f8dfa8506 100644
--- a/dom/base/nsTextNode.cpp
+++ b/dom/base/nsTextNode.cpp
@@ -240,7 +240,7 @@ void nsAttributeTextNode::AttributeChanged(Element* aElement,
   }
 }
 
-void nsAttributeTextNode::NodeWillBeDestroyed(nsINode* aNode) {
+void nsAttributeTextNode::NodeWillBeDestroyed(const nsINode* aNode) {
   NS_ASSERTION(aNode == static_cast<nsINode*>(mGrandparent), "Wrong node!");
   mGrandparent = nullptr;
 }
diff --git a/dom/html/HTMLTableElement.cpp b/dom/html/HTMLTableElement.cpp
index d6fc1573c277..24a4097445c2 100644
--- a/dom/html/HTMLTableElement.cpp
+++ b/dom/html/HTMLTableElement.cpp
@@ -489,7 +489,7 @@ void TableRowsCollection::ContentRemoved(nsIContent* aChild,
   }
 }
 
-void TableRowsCollection::NodeWillBeDestroyed(nsINode* aNode) {
+void TableRowsCollection::NodeWillBeDestroyed(const nsINode* aNode) {
   // Set mInitialized to false so CleanUp doesn't try to remove our mutation
   // observer, as we're going away. CleanUp() will reset mInitialized to true as
   // it returns.
diff --git a/dom/svg/SVGUseElement.cpp b/dom/svg/SVGUseElement.cpp
index b2382baef0ab..25521a5ba857 100644
--- a/dom/svg/SVGUseElement.cpp
+++ b/dom/svg/SVGUseElement.cpp
@@ -236,7 +236,7 @@ void SVGUseElement::ContentRemoved(nsIContent* aChild,
   }
 }
 
-void SVGUseElement::NodeWillBeDestroyed(nsINode* aNode) {
+void SVGUseElement::NodeWillBeDestroyed(const nsINode* aNode) {
   nsCOMPtr<nsIMutationObserver> kungFuDeathGrip(this);
   UnlinkSource();
 }
diff --git a/dom/xml/nsXMLPrettyPrinter.cpp b/dom/xml/nsXMLPrettyPrinter.cpp
index 4a386e92fbec..0e02054eac55 100644
--- a/dom/xml/nsXMLPrettyPrinter.cpp
+++ b/dom/xml/nsXMLPrettyPrinter.cpp
@@ -177,7 +177,7 @@ void nsXMLPrettyPrinter::ContentRemoved(nsIContent* aChild,
   MaybeUnhook(aChild->GetParent());
 }
 
-void nsXMLPrettyPrinter::NodeWillBeDestroyed(nsINode* aNode) {
+void nsXMLPrettyPrinter::NodeWillBeDestroyed(const nsINode* aNode) {
   mDocument = nullptr;
   NS_RELEASE_THIS();
 }
diff --git a/dom/xslt/xpath/XPathResult.cpp b/dom/xslt/xpath/XPathResult.cpp
index 091a83528ff7..f6ffd6d05d49 100644
--- a/dom/xslt/xpath/XPathResult.cpp
+++ b/dom/xslt/xpath/XPathResult.cpp
@@ -96,7 +96,7 @@ nsINode* XPathResult::IterateNext(ErrorResult& aRv) {
   return mResultNodes.SafeElementAt(mCurrentPos++);
 }
 
-void XPathResult::NodeWillBeDestroyed(nsINode* aNode) {
+void XPathResult::NodeWillBeDestroyed(const nsINode* aNode) {
   nsCOMPtr<nsIMutationObserver> kungFuDeathGrip(this);
   // Set to null to avoid unregistring unnecessarily
   mDocument = nullptr;
diff --git a/dom/xslt/xslt/txMozillaXSLTProcessor.cpp b/dom/xslt/xslt/txMozillaXSLTProcessor.cpp
index f3d4272e6f36..fd7fb2b9d4eb 100644
--- a/dom/xslt/xslt/txMozillaXSLTProcessor.cpp
+++ b/dom/xslt/xslt/txMozillaXSLTProcessor.cpp
@@ -1052,7 +1052,7 @@ nsresult txMozillaXSLTProcessor::ensureStylesheet() {
   return TX_CompileStylesheet(style, this, getter_AddRefs(mStylesheet));
 }
 
-void txMozillaXSLTProcessor::NodeWillBeDestroyed(nsINode* aNode) {
+void txMozillaXSLTProcessor::NodeWillBeDestroyed(const nsINode* aNode) {
   nsCOMPtr<nsIMutationObserver> kungFuDeathGrip(this);
   if (NS_FAILED(mCompileResult)) {
     return;
diff --git a/dom/xul/ChromeObserver.cpp b/dom/xul/ChromeObserver.cpp
index 4a21fdbbbb66..d5edd4fa4afe 100644
--- a/dom/xul/ChromeObserver.cpp
+++ b/dom/xul/ChromeObserver.cpp
@@ -199,7 +199,7 @@ void ChromeObserver::AttributeChanged(dom::Element* aElement,
   }
 }
 
-void ChromeObserver::NodeWillBeDestroyed(nsINode* aNode) {
+void ChromeObserver::NodeWillBeDestroyed(const nsINode* aNode) {
   mDocument = nullptr;
 }
 
diff --git a/editor/libeditor/HTMLAnonymousNodeEditor.cpp b/editor/libeditor/HTMLAnonymousNodeEditor.cpp
index 4c83c0a22e6b..f5315628aa24 100644
--- a/editor/libeditor/HTMLAnonymousNodeEditor.cpp
+++ b/editor/libeditor/HTMLAnonymousNodeEditor.cpp
@@ -115,7 +115,7 @@ void ElementDeletionObserver::ParentChainChanged(nsIContent* aContent) {
   NS_RELEASE_THIS();
 }
 
-void ElementDeletionObserver::NodeWillBeDestroyed(nsINode* aNode) {
+void ElementDeletionObserver::NodeWillBeDestroyed(const nsINode* aNode) {
   NS_ASSERTION(aNode == mNativeAnonNode || aNode == mObservedElement,
                "Wrong aNode!");
   if (aNode == mNativeAnonNode) {
diff --git a/layout/base/nsDocumentViewer.cpp b/layout/base/nsDocumentViewer.cpp
index de354dee5f2b..a888d62a7abd 100644
--- a/layout/base/nsDocumentViewer.cpp
+++ b/layout/base/nsDocumentViewer.cpp
@@ -276,7 +276,7 @@ void BFCachePreventionObserver::ContentRemoved(nsIContent* aChild,
   MutationHappened();
 }
 
-void BFCachePreventionObserver::NodeWillBeDestroyed(nsINode* aNode) {
+void BFCachePreventionObserver::NodeWillBeDestroyed(const nsINode* aNode) {
   mDocument = nullptr;
 }
 
diff --git a/layout/xul/tree/nsTreeContentView.cpp b/layout/xul/tree/nsTreeContentView.cpp
index edb5368e2abf..777fa884c820 100644
--- a/layout/xul/tree/nsTreeContentView.cpp
+++ b/layout/xul/tree/nsTreeContentView.cpp
@@ -955,7 +955,7 @@ void nsTreeContentView::ContentRemoved(nsIContent* aChild,
   }
 }
 
-void nsTreeContentView::NodeWillBeDestroyed(nsINode* aNode) {
+void nsTreeContentView::NodeWillBeDestroyed(const nsINode* aNode) {
   // XXXbz do we need this strong ref?  Do we drop refs to self in ClearRows?
   nsCOMPtr<nsIMutationObserver> kungFuDeathGrip(this);
   ClearRows();
diff --git a/toolkit/components/satchel/nsFormFillController.cpp b/toolkit/components/satchel/nsFormFillController.cpp
index 774224bb1da0..70312fa51477 100644
--- a/toolkit/components/satchel/nsFormFillController.cpp
+++ b/toolkit/components/satchel/nsFormFillController.cpp
@@ -200,11 +200,10 @@ void nsFormFillController::NativeAnonymousChildListChange(nsIContent* aContent,
 void nsFormFillController::ParentChainChanged(nsIContent* aContent) {}
 
 MOZ_CAN_RUN_SCRIPT_BOUNDARY
-void nsFormFillController::NodeWillBeDestroyed(nsINode* aNode) {
+void nsFormFillController::NodeWillBeDestroyed(const nsINode* aNode) {
   MOZ_LOG(sLogger, LogLevel::Verbose, ("NodeWillBeDestroyed: %p", aNode));
   mPwmgrInputs.Remove(aNode);
   mAutofillInputs.Remove(aNode);
-  MaybeRemoveMutationObserver(aNode);
   if (aNode == mListNode) {
     mListNode = nullptr;
     RevalidateDataList();
diff --git a/widget/cocoa/nsMenuGroupOwnerX.mm b/widget/cocoa/nsMenuGroupOwnerX.mm
index 5eb8b050fc5e..b5afb18023c9 100644
--- a/widget/cocoa/nsMenuGroupOwnerX.mm
+++ b/widget/cocoa/nsMenuGroupOwnerX.mm
@@ -53,7 +53,7 @@ void nsMenuGroupOwnerX::ContentAppended(nsIContent* aFirstNewContent) {
   }
 }
 
-void nsMenuGroupOwnerX::NodeWillBeDestroyed(nsINode* aNode) {}
+void nsMenuGroupOwnerX::NodeWillBeDestroyed(const nsINode* aNode) {}
 
 void nsMenuGroupOwnerX::AttributeWillChange(dom::Element* aElement, int32_t aNameSpaceID,
                                             nsAtom* aAttribute, int32_t aModType) {}