diff --git a/content/html/content/src/nsGenericHTMLElement.cpp b/content/html/content/src/nsGenericHTMLElement.cpp
index 4f2dcfe12b51..ea705df3f085 100644
--- a/content/html/content/src/nsGenericHTMLElement.cpp
+++ b/content/html/content/src/nsGenericHTMLElement.cpp
@@ -721,6 +721,26 @@ nsGenericHTMLElement::GetInnerHTML(nsAString& aInnerHTML)
   return rv;
 }
 
+void
+nsGenericHTMLElement::FireMutationEventsForDirectParsing(nsIDocument* aDoc,
+                                                         nsIContent* aDest,
+                                                         PRInt32 aOldChildCount)
+{
+  // Fire mutation events. Optimize for the case when there are no listeners
+  PRInt32 newChildCount = aDest->GetChildCount();
+  if (newChildCount && nsContentUtils::
+        HasMutationListeners(aDoc, NS_EVENT_BITS_MUTATION_NODEINSERTED)) {
+    nsAutoTArray<nsCOMPtr<nsIContent>, 50> childNodes;
+    NS_ASSERTION(newChildCount - aOldChildCount >= 0,
+                 "What, some unexpected dom mutation has happened?");
+    childNodes.SetCapacity(newChildCount - aOldChildCount);
+    for (nsINode::ChildIterator iter(aDest); !iter.IsDone(); iter.Next()) {
+      childNodes.AppendElement(iter);
+    }
+    nsGenericElement::FireNodeInserted(aDoc, aDest, childNodes);
+  }
+}
+
 nsresult
 nsGenericHTMLElement::SetInnerHTML(const nsAString& aInnerHTML)
 {
@@ -755,19 +775,7 @@ nsGenericHTMLElement::SetInnerHTML(const nsAString& aInnerHTML)
                                           eCompatibility_NavQuirks,
                                       PR_TRUE);
     // HTML5 parser has notified, but not fired mutation events.
-    // Fire mutation events. Optimize for the case when there are no listeners
-    PRInt32 newChildCount = GetChildCount();
-    if (newChildCount && nsContentUtils::
-          HasMutationListeners(doc, NS_EVENT_BITS_MUTATION_NODEINSERTED)) {
-      nsAutoTArray<nsCOMPtr<nsIContent>, 50> childNodes;
-      NS_ASSERTION(newChildCount - oldChildCount >= 0,
-                   "What, some unexpected dom mutation has happened?");
-      childNodes.SetCapacity(newChildCount - oldChildCount);
-      for (nsINode::ChildIterator iter(this); !iter.IsDone(); iter.Next()) {
-        childNodes.AppendElement(iter);
-      }
-      nsGenericElement::FireNodeInserted(doc, this, childNodes);
-    }
+    FireMutationEventsForDirectParsing(doc, this, oldChildCount);
   } else {
     rv = nsContentUtils::CreateContextualFragment(this, aInnerHTML,
                                                   PR_TRUE,
@@ -781,6 +789,104 @@ nsGenericHTMLElement::SetInnerHTML(const nsAString& aInnerHTML)
   return rv;
 }
 
+enum nsAdjacentPosition {
+  eBeforeBegin,
+  eAfterBegin,
+  eBeforeEnd,
+  eAfterEnd
+};
+
+nsresult
+nsGenericHTMLElement::InsertAdjacentHTML(const nsAString& aPosition,
+                                         const nsAString& aText)
+{
+  nsAdjacentPosition position;
+  if (aPosition.LowerCaseEqualsLiteral("beforebegin")) {
+    position = eBeforeBegin;
+  } else if (aPosition.LowerCaseEqualsLiteral("afterbegin")) {
+    position = eAfterBegin;
+  } else if (aPosition.LowerCaseEqualsLiteral("beforeend")) {
+    position = eBeforeEnd;
+  } else if (aPosition.LowerCaseEqualsLiteral("afterend")) {
+    position = eAfterEnd;
+  } else {
+    return NS_ERROR_DOM_SYNTAX_ERR;
+  }
+
+  nsCOMPtr<nsIContent> destination;
+  if (position == eBeforeBegin || position == eAfterEnd) {
+    destination = GetParent();
+    if (!destination) {
+      return NS_ERROR_DOM_NO_MODIFICATION_ALLOWED_ERR;
+    }
+  } else {
+    destination = this;
+  }
+
+  nsIDocument* doc = GetOwnerDoc();
+  NS_ENSURE_STATE(doc);
+
+  // Needed when insertAdjacentHTML is used in combination with contenteditable
+  mozAutoDocUpdate updateBatch(doc, UPDATE_CONTENT_MODEL, PR_TRUE);
+
+  // Batch possible DOMSubtreeModified events.
+  mozAutoSubtreeModified subtree(doc, nsnull);
+
+  // Parse directly into destination if possible
+  if (doc->IsHTML() &&
+      (position == eBeforeEnd ||
+       (position == eAfterEnd && !GetNextSibling()) ||
+       (position == eAfterBegin && !GetFirstChild()))) {
+    PRInt32 oldChildCount = destination->GetChildCount();
+    PRInt32 contextNs = destination->GetNameSpaceID();
+    nsIAtom* contextLocal = destination->Tag();
+    if (contextLocal == nsGkAtoms::html && contextNs == kNameSpaceID_XHTML) {
+      // For compat with IE6 through IE9. Willful violation of HTML5 as of
+      // 2011-04-06. CreateContextualFragment does the same already.
+      // Spec bug: http://www.w3.org/Bugs/Public/show_bug.cgi?id=12434
+      contextLocal = nsGkAtoms::body;
+    }
+    nsContentUtils::ParseFragmentHTML(aText,
+                                      destination,
+                                      contextLocal,
+                                      contextNs,
+                                      doc->GetCompatibilityMode() ==
+                                          eCompatibility_NavQuirks,
+                                      PR_TRUE);
+    // HTML5 parser has notified, but not fired mutation events.
+    FireMutationEventsForDirectParsing(doc, destination, oldChildCount);
+    return NS_OK;
+  }
+
+  // couldn't parse directly
+  nsCOMPtr<nsIDOMDocumentFragment> df;
+  nsresult rv = nsContentUtils::CreateContextualFragment(destination,
+                                                         aText,
+                                                         PR_TRUE,
+                                                         getter_AddRefs(df));
+  nsCOMPtr<nsINode> fragment = do_QueryInterface(df);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  switch (position) {
+    case eBeforeBegin:
+      destination->InsertBefore(fragment, this, &rv);
+      break;
+    case eAfterBegin:
+      static_cast<nsINode*>(this)->InsertBefore(fragment, GetFirstChild(), &rv);
+      break;
+    case eBeforeEnd:
+      static_cast<nsINode*>(this)->AppendChild(fragment, &rv);
+      break;
+    case eAfterEnd:
+      destination->InsertBefore(fragment, GetNextSibling(), &rv);
+      break;
+    default:
+      NS_NOTREACHED("Bad position.");
+      break;
+  }
+  return rv;
+}
+
 nsresult
 nsGenericHTMLElement::ScrollIntoView(PRBool aTop, PRUint8 optional_argc)
 {
diff --git a/content/html/content/src/nsGenericHTMLElement.h b/content/html/content/src/nsGenericHTMLElement.h
index c4c5313a2fbd..af428736e755 100644
--- a/content/html/content/src/nsGenericHTMLElement.h
+++ b/content/html/content/src/nsGenericHTMLElement.h
@@ -135,6 +135,8 @@ public:
   nsresult GetOffsetParent(nsIDOMElement** aOffsetParent);
   virtual nsresult GetInnerHTML(nsAString& aInnerHTML);
   virtual nsresult SetInnerHTML(const nsAString& aInnerHTML);
+  virtual nsresult InsertAdjacentHTML(const nsAString& aPosition,
+                                      const nsAString& aText);
   nsresult ScrollIntoView(PRBool aTop, PRUint8 optional_argc);
   // Declare Focus(), Blur(), GetTabIndex(), SetTabIndex(), GetHidden(),
   // SetHidden(), GetSpellcheck(), SetSpellcheck(), and GetDraggable() such that
@@ -571,6 +573,18 @@ protected:
   }
 
 private:
+  /**
+   * Fire mutation events for changes caused by parsing directly into a
+   * context node.
+   *
+   * @param aDoc the document of the node
+   * @param aDest the destination node that got stuff appended to it
+   * @param aOldChildCount the number of children the node had before parsing
+   */
+  void FireMutationEventsForDirectParsing(nsIDocument* aDoc,
+                                          nsIContent* aDest,
+                                          PRInt32 aOldChildCount);
+
   void RegUnRegAccessKey(PRBool aDoReg);
 
 protected:
diff --git a/dom/interfaces/html/nsIDOMNSHTMLElement.idl b/dom/interfaces/html/nsIDOMNSHTMLElement.idl
index 88dbedb3265a..0000b619d2ec 100644
--- a/dom/interfaces/html/nsIDOMNSHTMLElement.idl
+++ b/dom/interfaces/html/nsIDOMNSHTMLElement.idl
@@ -40,7 +40,7 @@
 
 interface nsIDOMDOMStringMap;
 
-[scriptable, uuid(cf76761d-2d93-4e88-aaf1-b637878bad65)]
+[scriptable, uuid(4012e9a9-f6fb-48b3-9a80-b096c1dcb5ba)]
 interface nsIDOMNSHTMLElement : nsISupports
 {
   readonly attribute long             offsetTop;
@@ -65,6 +65,10 @@ interface nsIDOMNSHTMLElement : nsISupports
            // for WHAT-WG drag and drop
            attribute boolean          draggable;
 
+  void insertAdjacentHTML(in DOMString position,
+                          in DOMString text)
+                          raises(DOMException);
+
   [optional_argc] void scrollIntoView([optional] in boolean top);
 
            attribute boolean         spellcheck;