--- a/editor/libeditor/HTMLEditor.cpp
+++ b/editor/libeditor/HTMLEditor.cpp
@@ -743,38 +743,58 @@ HTMLEditor::IsBlockNode(nsINode* aNode)
 {
   return aNode && NodeIsBlockStatic(aNode);
 }
 
 /**
  * GetBlockNodeParent returns enclosing block level ancestor, if any.
  */
 Element*
-HTMLEditor::GetBlockNodeParent(nsINode* aNode)
+HTMLEditor::GetBlockNodeParent(nsINode* aNode,
+                               nsINode* aAncestorLimiter)
 {
   MOZ_ASSERT(aNode);
+  MOZ_ASSERT(!aAncestorLimiter ||
+             aNode == aAncestorLimiter ||
+             EditorUtils::IsDescendantOf(aNode, aAncestorLimiter),
+             "aNode isn't in aAncestorLimiter");
+
+  // The caller has already reached the limiter.
+  if (aNode == aAncestorLimiter) {
+    return nullptr;
+  }
 
   nsCOMPtr<nsINode> p = aNode->GetParentNode();
 
   while (p) {
     if (NodeIsBlockStatic(p)) {
       return p->AsElement();
     }
+    // Now, we have reached the limiter, there is no block in its ancestors.
+    if (p == aAncestorLimiter) {
+      return nullptr;
+    }
     p = p->GetParentNode();
   }
 
   return nullptr;
 }
 
 /**
  * Returns the node if it's a block, otherwise GetBlockNodeParent
  */
 Element*
-HTMLEditor::GetBlock(nsINode& aNode)
+HTMLEditor::GetBlock(nsINode& aNode,
+                     nsINode* aAncestorLimiter)
 {
+  MOZ_ASSERT(!aAncestorLimiter ||
+             &aNode == aAncestorLimiter ||
+             EditorUtils::IsDescendantOf(&aNode, aAncestorLimiter),
+             "aNode isn't in aAncestorLimiter");
+
   if (NodeIsBlockStatic(&aNode)) {
     return aNode.AsElement();
   }
   return GetBlockNodeParent(&aNode);
 }
 
 /**
  * IsNextCharInNodeWhitespace() checks the adjacent content in the same node to

--- a/editor/libeditor/HTMLEditor.h
+++ b/editor/libeditor/HTMLEditor.h
@@ -180,19 +180,30 @@ public:
 
   /**
    * This sets background on the appropriate container element (table, cell,)
    * or calls into nsTextEditor to set the page background.
    */
   nsresult SetCSSBackgroundColor(const nsAString& aColor);
   nsresult SetHTMLBackgroundColor(const nsAString& aColor);
 
-  // Block methods moved from EditorBase
-  static Element* GetBlockNodeParent(nsINode* aNode);
-  static Element* GetBlock(nsINode& aNode);
+  /**
+   * GetBlockNodeParent() returns parent or nearest ancestor of aNode if
+   * there is a block parent.  If aAncestorLimiter is not nullptr,
+   * this stops looking for the result.
+   */
+  static Element* GetBlockNodeParent(nsINode* aNode,
+                                     nsINode* aAncestorLimiter = nullptr);
+  /**
+   * GetBlock() returns aNode itself, or parent or nearest ancestor of aNode
+   * if there is a block parent.  If aAncestorLimiter is not nullptr,
+   * this stops looking for the result.
+   */
+  static Element* GetBlock(nsINode& aNode,
+                           nsINode* aAncestorLimiter = nullptr);
 
   void IsNextCharInNodeWhitespace(nsIContent* aContent,
                                   int32_t aOffset,
                                   bool* outIsSpace,
                                   bool* outIsNBSP,
                                   nsIContent** outNode = nullptr,
                                   int32_t* outOffset = 0);
   void IsPrevCharInNodeWhitespace(nsIContent* aContent,