--- a/dom/base/Comment.cpp
+++ b/dom/base/Comment.cpp
@@ -20,22 +20,16 @@ namespace mozilla {
 namespace dom {
 
 Comment::~Comment()
 {
 }
 
 NS_IMPL_ISUPPORTS_INHERITED(Comment, CharacterData, nsIDOMNode)
 
-bool
-Comment::IsNodeOfType(uint32_t aFlags) const
-{
-  return !(aFlags & ~eCOMMENT);
-}
-
 already_AddRefed<CharacterData>
 Comment::CloneDataNode(mozilla::dom::NodeInfo *aNodeInfo, bool aCloneText) const
 {
   RefPtr<mozilla::dom::NodeInfo> ni = aNodeInfo;
   RefPtr<Comment> it = new Comment(ni.forget());
   if (aCloneText) {
     it->mText = mText;
   }

--- a/dom/base/Comment.h
+++ b/dom/base/Comment.h
@@ -34,22 +34,21 @@ public:
   }
 
   explicit Comment(nsNodeInfoManager* aNodeInfoManager)
     : CharacterData(aNodeInfoManager->GetCommentNodeInfo())
   {
     Init();
   }
 
+  NS_IMPL_FROMNODE_HELPER(Comment, IsComment())
+
   // nsISupports
   NS_DECL_ISUPPORTS_INHERITED
 
-  // nsINode
-  virtual bool IsNodeOfType(uint32_t aFlags) const override;
-
   virtual already_AddRefed<CharacterData>
     CloneDataNode(mozilla::dom::NodeInfo *aNodeInfo,
                   bool aCloneText) const override;
 
   virtual nsIDOMNode* AsDOMNode() override { return this; }
 #ifdef DEBUG
   virtual void List(FILE* out, int32_t aIndent) const override;
   virtual void DumpContent(FILE* out = stdout, int32_t aIndent = 0,

--- a/dom/base/nsINode.h
+++ b/dom/base/nsINode.h
@@ -411,18 +411,16 @@ public:
   /**
    * Bit-flags to pass (or'ed together) to IsNodeOfType()
    */
   enum {
     /** nsIAttribute nodes */
     eATTRIBUTE           = 1 << 2,
     /** xml processing instructions */
     ePROCESSING_INSTRUCTION = 1 << 4,
-    /** comment nodes */
-    eCOMMENT             = 1 << 5,
     /** form control elements */
     eHTML_FORM_CONTROL   = 1 << 6,
     /** animation elements */
     eANIMATION           = 1 << 10,
     /** filter elements that implement SVGFilterPrimitiveStandardAttributes */
     eFILTER              = 1 << 11,
     /** SVGGeometryElement */
     eSHAPE               = 1 << 12
@@ -572,16 +570,24 @@ public:
   {
     uint32_t nodeType = NodeType();
     return nodeType == TEXT_NODE ||
            nodeType == CDATA_SECTION_NODE ||
            nodeType == PROCESSING_INSTRUCTION_NODE ||
            nodeType == COMMENT_NODE;
   }
 
+  /**
+   * Return whether the node is a Comment node.
+   */
+  bool IsComment() const
+  {
+    return NodeType() == COMMENT_NODE;
+  }
+
   virtual nsIDOMNode* AsDOMNode() = 0;
 
   /**
    * Return if this node has any children.
    */
   bool HasChildren() const { return !!mFirstChild; }
 
   /**

--- a/dom/base/nsTreeSanitizer.cpp
+++ b/dom/base/nsTreeSanitizer.cpp
@@ -1494,17 +1494,17 @@ nsTreeSanitizer::SanitizeChildren(nsINod
                            false,
                            false);
       }
       node = node->GetNextNode(aRoot);
       continue;
     }
     NS_ASSERTION(!node->GetFirstChild(), "How come non-element node had kids?");
     nsIContent* next = node->GetNextNonChildNode(aRoot);
-    if (!mAllowComments && node->IsNodeOfType(nsINode::eCOMMENT)) {
+    if (!mAllowComments && node->IsComment()) {
       node->RemoveFromParent();
     }
     node = next;
   }
 }
 
 void
 nsTreeSanitizer::RemoveAllAttributes(Element* aElement)

--- a/dom/xslt/xpath/txXPathTreeWalker.h
+++ b/dom/xslt/xpath/txXPathTreeWalker.h
@@ -240,18 +240,17 @@ txXPathNodeUtils::isProcessingInstructio
     return aNode.isContent() &&
            aNode.Content()->IsNodeOfType(nsINode::ePROCESSING_INSTRUCTION);
 }
 
 /* static */
 inline bool
 txXPathNodeUtils::isComment(const txXPathNode& aNode)
 {
-    return aNode.isContent() &&
-           aNode.Content()->IsNodeOfType(nsINode::eCOMMENT);
+    return aNode.isContent() && aNode.Content()->IsComment();
 }
 
 /* static */
 inline bool
 txXPathNodeUtils::isText(const txXPathNode& aNode)
 {
     return aNode.isContent() &&
            aNode.Content()->IsText();

--- a/editor/libeditor/HTMLEditorDataTransfer.cpp
+++ b/editor/libeditor/HTMLEditorDataTransfer.cpp
@@ -1986,19 +1986,19 @@ nsresult FindTargetNode(nsINode *aStart,
     if (!aResult) {
       aResult = aStart;
     }
     return NS_OK;
   }
 
   do {
     // Is this child the magical cookie?
-    if (child->IsNodeOfType(nsINode::eCOMMENT)) {
+    if (auto* comment = Comment::FromNode(child)) {
       nsAutoString data;
-      static_cast<Comment*>(child.get())->GetData(data);
+      comment->GetData(data);
 
       if (data.EqualsLiteral(kInsertCookie)) {
         // Yes it is! Return an error so we bubble out and short-circuit the
         // search.
         aResult = aStart;
 
         child->Remove();
 

--- a/layout/base/nsCSSFrameConstructor.cpp
+++ b/layout/base/nsCSSFrameConstructor.cpp
@@ -5509,17 +5509,17 @@ nsCSSFrameConstructor::ShouldCreateItems
   }
 
   // don't create a whitespace frame if aParent doesn't want it
   if (!NeedFrameFor(aState, aParentFrame, aContent)) {
     return false;
   }
 
   // never create frames for comments or PIs
-  if (aContent->IsNodeOfType(nsINode::eCOMMENT) ||
+  if (aContent->IsComment() ||
       aContent->IsNodeOfType(nsINode::ePROCESSING_INSTRUCTION)) {
     return false;
   }
 
   return true;
 }
 
 void
@@ -6345,17 +6345,17 @@ nsCSSFrameConstructor::IsValidSibling(ns
       StyleDisplay::TableCaption     == siblingDisplay ||
       StyleDisplay::TableHeaderGroup == siblingDisplay ||
       StyleDisplay::TableRowGroup    == siblingDisplay ||
       StyleDisplay::TableFooterGroup == siblingDisplay ||
       LayoutFrameType::Menu == parentType) {
     // if we haven't already, resolve a style to find the display type of
     // aContent.
     if (UNSET_DISPLAY == aDisplay) {
-      if (aContent->IsNodeOfType(nsINode::eCOMMENT) ||
+      if (aContent->IsComment() ||
           aContent->IsNodeOfType(nsINode::ePROCESSING_INSTRUCTION)) {
         // Comments and processing instructions never have frames, so we should
         // not try to generate styles for them.
         return false;
       }
       // FIXME(emilio): This is buggy some times, see bug 1424656.
       RefPtr<ComputedStyle> computedStyle = ResolveComputedStyle(aContent);
       const nsStyleDisplay* display = computedStyle->StyleDisplay();
@@ -10103,17 +10103,17 @@ nsCSSFrameConstructor::AddFCItemsForAnon
     nsIContent* content = aAnonymousItems[i].mContent;
     // Gecko-styled nodes should have no pending restyle flags.
     // Assert some things about this content
     MOZ_ASSERT(!(content->GetFlags() &
                  (NODE_DESCENDANTS_NEED_FRAMES | NODE_NEEDS_FRAME)),
                "Should not be marked as needing frames");
     MOZ_ASSERT(!content->GetPrimaryFrame(),
                "Should have no existing frame");
-    MOZ_ASSERT(!content->IsNodeOfType(nsINode::eCOMMENT) &&
+    MOZ_ASSERT(!content->IsComment() &&
                !content->IsNodeOfType(nsINode::ePROCESSING_INSTRUCTION),
                "Why is someone creating garbage anonymous content");
 
     // Make sure we eagerly performed the servo cascade when the anonymous
     // nodes were created.
     MOZ_ASSERT(!content->IsElement() || content->AsElement()->HasServoData());
 
     RefPtr<ComputedStyle> computedStyle = ResolveComputedStyle(content);
@@ -11450,17 +11450,17 @@ nsCSSFrameConstructor::BuildInlineChildI
   } else {
     // Use the content tree child list:
     FlattenedChildIterator iter(parentContent);
     for (nsIContent* content = iter.GetNextChild(); content; content = iter.GetNextChild()) {
       // Manually check for comments/PIs, since we don't have a frame to pass to
       // AddFrameConstructionItems.  We know our parent is a non-replaced inline,
       // so there is no need to do the NeedFrameFor check.
       content->UnsetFlags(NODE_DESCENDANTS_NEED_FRAMES | NODE_NEEDS_FRAME);
-      if (content->IsNodeOfType(nsINode::eCOMMENT) ||
+      if (content->IsComment() ||
           content->IsNodeOfType(nsINode::ePROCESSING_INSTRUCTION)) {
         continue;
       }
 
       RefPtr<ComputedStyle> childContext = ResolveComputedStyle(content);
       AddFrameConstructionItemsInternal(aState, content, nullptr,
                                         iter.XBLInvolved(), childContext,
                                         flags, nullptr,

--- a/layout/style/nsStyleUtil.cpp
+++ b/layout/style/nsStyleUtil.cpp
@@ -741,33 +741,33 @@ nsStyleUtil::ColorComponentToFloat(uint8
 }
 
 /* static */ bool
 nsStyleUtil::IsSignificantChild(nsIContent* aChild,
                                 bool aWhitespaceIsSignificant)
 {
   bool isText = aChild->IsText();
 
-  if (!isText && !aChild->IsNodeOfType(nsINode::eCOMMENT) &&
+  if (!isText && !aChild->IsComment() &&
       !aChild->IsNodeOfType(nsINode::ePROCESSING_INSTRUCTION)) {
     return true;
   }
 
   return isText && aChild->TextLength() != 0 &&
          (aWhitespaceIsSignificant ||
           !aChild->TextIsOnlyWhitespace());
 }
 
 /* static */ bool
 nsStyleUtil::ThreadSafeIsSignificantChild(const nsIContent* aChild,
                                           bool aWhitespaceIsSignificant)
 {
   bool isText = aChild->IsText();
 
-  if (!isText && !aChild->IsNodeOfType(nsINode::eCOMMENT) &&
+  if (!isText && !aChild->IsComment() &&
       !aChild->IsNodeOfType(nsINode::ePROCESSING_INSTRUCTION)) {
     return true;
   }
 
   return isText && aChild->TextLength() != 0 &&
          (aWhitespaceIsSignificant ||
           !aChild->ThreadSafeTextIsOnlyWhitespace());
 }

--- a/toolkit/components/find/nsFind.cpp
+++ b/toolkit/components/find/nsFind.cpp
@@ -854,27 +854,27 @@ nsFind::IsVisibleNode(nsINode* aDOMNode)
 }
 
 bool
 nsFind::SkipNode(nsIContent* aContent)
 {
 #ifdef HAVE_BIDI_ITERATOR
   // We may not need to skip comment nodes, now that IsTextNode distinguishes
   // them from real text nodes.
-  return aContent->IsNodeOfType(nsINode::eCOMMENT) ||
+  return aContent->IsComment() ||
          aContent->IsAnyOfHTMLElements(sScriptAtom, sNoframesAtom, sSelectAtom);
 
 #else /* HAVE_BIDI_ITERATOR */
   // Temporary: eventually we will have an iterator to do this, but for now, we
   // have to climb up the tree for each node and see whether any parent is a
   // skipped node, and take the performance hit.
 
   nsIContent* content = aContent;
   while (content) {
-    if (aContent->IsNodeOfType(nsINode::eCOMMENT) ||
+    if (aContent->IsComment() ||
         content->IsAnyOfHTMLElements(nsGkAtoms::script,
                                      nsGkAtoms::noframes,
                                      nsGkAtoms::select)) {
 #ifdef DEBUG_FIND
       printf("Skipping node: ");
       nsCOMPtr<nsIDOMNode> node(do_QueryInterface(content));
       DumpNode(node);
 #endif