--- a/editor/libeditor/HTMLEditRules.cpp
+++ b/editor/libeditor/HTMLEditRules.cpp
@@ -1797,21 +1797,17 @@ HTMLEditRules::WillInsertBreak(Selection
   //     Gmail.  So, let's use traditional odd behavior only when the default
   //     paragraph separator is <br>.  Otherwise, take consistent behavior
   //     between <p> container and <div> container.
   if ((separator == ParagraphSeparator::br &&
        blockParent->IsHTMLElement(nsGkAtoms::p)) ||
       (separator != ParagraphSeparator::br &&
        blockParent->IsAnyOfHTMLElements(nsGkAtoms::p, nsGkAtoms::div))) {
     // Paragraphs: special rules to look for <br>s
-    EditActionResult result =
-      ReturnInParagraph(aSelection, *blockParent,
-                        atStartOfSelection.Container(),
-                        atStartOfSelection.Offset(),
-                        atStartOfSelection.GetChildAtOffset());
+    EditActionResult result = ReturnInParagraph(aSelection, *blockParent);
     if (NS_WARN_IF(result.Failed())) {
       return result.Rv();
     }
     *aHandled = result.Handled();
     *aCancel = result.Canceled();
     // Fall through, we may not have handled it in ReturnInParagraph()
   }
 
@@ -6729,72 +6725,77 @@ HTMLEditRules::ReturnInHeader(Selection&
     rv = aSelection.Collapse(&aHeader, 0);
     NS_ENSURE_SUCCESS(rv, rv);
   }
   return NS_OK;
 }
 
 EditActionResult
 HTMLEditRules::ReturnInParagraph(Selection& aSelection,
-                                 nsINode& aParentDivOrP,
-                                 nsINode* aNode,
-                                 int32_t aOffset,
-                                 nsIContent* aChildAtOffset)
+                                 nsINode& aParentDivOrP)
 {
   if (NS_WARN_IF(!mHTMLEditor)) {
     return EditActionResult(NS_ERROR_NOT_AVAILABLE);
   }
 
-  nsCOMPtr<nsINode> node = do_QueryInterface(aNode);
-  if (!node) {
-    return EditActionResult(NS_ERROR_NULL_POINTER);
-  }
-
   RefPtr<HTMLEditor> htmlEditor = mHTMLEditor;
 
+  nsRange* firstRange = aSelection.GetRangeAt(0);
+  if (NS_WARN_IF(!firstRange)) {
+    return EditActionResult(NS_ERROR_FAILURE);
+  }
+
+  EditorDOMPoint atStartOfSelection(firstRange->StartRef());
+  if (NS_WARN_IF(!atStartOfSelection.IsSet())) {
+    return EditActionResult(NS_ERROR_FAILURE);
+  }
+  MOZ_ASSERT(atStartOfSelection.IsSetAndValid());
+
   bool doesCRCreateNewP = htmlEditor->GetReturnInParagraphCreatesNewParagraph();
 
   bool splitAfterNewBR = false;
   nsCOMPtr<nsIContent> brNode;
 
   // Point to split aParentDivOrP.
   // XXX If we don't need to use nsIDOMNode here, we should use EditorDOMPoint.
-  nsCOMPtr<nsIDOMNode> containerAtSplitPoint = GetAsDOMNode(aNode);
-  int32_t offsetAtSplitPoint = aOffset;
+  nsCOMPtr<nsIDOMNode> containerAtSplitPoint =
+    GetAsDOMNode(atStartOfSelection.Container());
+  int32_t offsetAtSplitPoint = atStartOfSelection.Offset();
 
   EditorRawDOMPoint pointToInsertBR;
-  if (aNode == &aParentDivOrP && doesCRCreateNewP) {
-    // We are at the edges of the block, we don't need to create new <br>.
+  if (doesCRCreateNewP &&
+      atStartOfSelection.Container() == &aParentDivOrP) {
+    // We are at the edges of the block, so, we don't need to create new <br>.
     brNode = nullptr;
-  } else if (EditorBase::IsTextNode(aNode)) {
+  } else if (EditorBase::IsTextNode(atStartOfSelection.Container())) {
     // at beginning of text node?
-    if (!aOffset) {
+    if (atStartOfSelection.IsStartOfContainer()) {
       // is there a BR prior to it?
-      brNode = htmlEditor->GetPriorHTMLSibling(node);
+      brNode = htmlEditor->GetPriorHTMLSibling(atStartOfSelection.Container());
       if (!brNode ||
           !htmlEditor->IsVisibleBRElement(brNode) ||
           TextEditUtils::HasMozAttr(GetAsDOMNode(brNode))) {
-        pointToInsertBR.Set(node);
+        pointToInsertBR.Set(atStartOfSelection.Container());
         brNode = nullptr;
       }
-    } else if (aOffset == static_cast<int32_t>(node->Length())) {
+    } else if (atStartOfSelection.IsEndOfContainer()) {
       // we're at the end of text node...
       // is there a BR after to it?
-      brNode = htmlEditor->GetNextHTMLSibling(node);
+      brNode = htmlEditor->GetNextHTMLSibling(atStartOfSelection.Container());
       if (!brNode ||
           !htmlEditor->IsVisibleBRElement(brNode) ||
           TextEditUtils::HasMozAttr(GetAsDOMNode(brNode))) {
-        pointToInsertBR.Set(node);
+        pointToInsertBR.Set(atStartOfSelection.Container());
         DebugOnly<bool> advanced = pointToInsertBR.AdvanceOffset();
         NS_WARNING_ASSERTION(advanced,
-          "Failed to advance offset to after the container");
+          "Failed to advance offset to after the container of selection start");
         brNode = nullptr;
       }
     } else {
-      nsCOMPtr<nsINode> leftNode = node;
+      nsCOMPtr<nsINode> leftNode = atStartOfSelection.Container();
 
       if (doesCRCreateNewP) {
         nsCOMPtr<nsIDOMNode> leftDOMNode;
         nsresult rv =
           htmlEditor->SplitNode(containerAtSplitPoint, offsetAtSplitPoint,
                                 getter_AddRefs(leftDOMNode));
         if (NS_WARN_IF(NS_FAILED(rv))) {
           return EditActionResult(rv);
@@ -6803,35 +6804,32 @@ HTMLEditRules::ReturnInParagraph(Selecti
         leftNode = do_QueryInterface(leftDOMNode);
       }
 
       // We need to put new <br> after the left node if given node was split
       // above.
       pointToInsertBR.Set(leftNode);
       DebugOnly<bool> advanced = pointToInsertBR.AdvanceOffset();
       NS_WARNING_ASSERTION(advanced,
-        "Failed to advance offset to after the container");
+        "Failed to advance offset to after the container of selection start");
     }
   } else {
     // not in a text node.
     // is there a BR prior to it?
     nsCOMPtr<nsIContent> nearNode;
-    nearNode = htmlEditor->GetPreviousEditableHTMLNode(
-                             EditorRawDOMPoint(node, aChildAtOffset, aOffset));
+    nearNode =
+      htmlEditor->GetPreviousEditableHTMLNode(atStartOfSelection.AsRaw());
     if (!nearNode || !htmlEditor->IsVisibleBRElement(nearNode) ||
         TextEditUtils::HasMozAttr(GetAsDOMNode(nearNode))) {
       // is there a BR after it?
       nearNode =
-        htmlEditor->GetNextEditableHTMLNode(
-                      EditorRawDOMPoint(node, aChildAtOffset, aOffset));
+        htmlEditor->GetNextEditableHTMLNode(atStartOfSelection.AsRaw());
       if (!nearNode || !htmlEditor->IsVisibleBRElement(nearNode) ||
           TextEditUtils::HasMozAttr(GetAsDOMNode(nearNode))) {
-        pointToInsertBR.Set(node, aOffset);
-        NS_WARNING_ASSERTION(pointToInsertBR.IsSetAndValid(),
-          "Failed to set point to insert <br> to given node");
+        pointToInsertBR = atStartOfSelection;
         splitAfterNewBR = true;
       }
     }
     if (!pointToInsertBR.IsSet() && TextEditUtils::IsBreak(nearNode)) {
       brNode = nearNode;
     }
   }
   if (pointToInsertBR.IsSet()) {

--- a/editor/libeditor/HTMLEditRules.h
+++ b/editor/libeditor/HTMLEditRules.h
@@ -292,32 +292,29 @@ protected:
                        Tables aTables = Tables::yes);
   Element* IsInListItem(nsINode* aNode);
   nsAtom& DefaultParagraphSeparator();
   nsresult ReturnInHeader(Selection& aSelection, Element& aHeader,
                           nsINode& aNode, int32_t aOffset);
 
   /**
    * ReturnInParagraph() does the right thing for Enter key press or
-   * 'insertParagraph' command in aParentDivOrP.
+   * 'insertParagraph' command in aParentDivOrP.  aParentDivOrP will be
+   * split at start of first selection range.
    *
-   * @param aSelection      The selection
+   * @param aSelection      The selection.  aParentDivOrP will be split at
+   *                        start of the first selection range.
    * @param aParentDivOrP   The parent block.  This must be <p> or <div>
    *                        element.
-   * @param aTextNode
-   * @param aOffset
-   * @param aChildAtOffset
    * @return                Returns with NS_OK if this doesn't meat any
    *                        unexpected situation.  If this method tries to
    *                        split the paragraph, marked as handled.
    */
   EditActionResult ReturnInParagraph(Selection& aSelection,
-                                     nsINode& aParentDivOrP,
-                                     nsINode* aTextNode, int32_t aOffset,
-                                     nsIContent* aChildAtOffset);
+                                     nsINode& aParentDivOrP);
 
   /**
    * SplitParagraph() splits the parent block, aPara, at aSelNode - aOffset.
    *
    * @param aPara       The parent block to be split.
    * @param aBRNode     Next <br> node if there is.  Otherwise, nullptr.
    *                    If this is not nullptr, the <br> node may be removed.
    * @param aSelection  The selection.