diff --git a/dom/base/Element.cpp b/dom/base/Element.cpp
index f097c643887e..b555cb0bce5d 100644
--- a/dom/base/Element.cpp
+++ b/dom/base/Element.cpp
@@ -4402,6 +4402,15 @@ Element::SetCustomElementData(CustomElementData* aData)
 {
   nsExtendedDOMSlots *slots = ExtendedDOMSlots();
   MOZ_ASSERT(!slots->mCustomElementData, "Custom element data may not be changed once set.");
+  #if DEBUG
+    nsAtom* name = NodeInfo()->NameAtom();
+    nsAtom* type = aData->GetCustomElementType();
+    if (nsContentUtils::IsCustomElementName(name)) {
+      MOZ_ASSERT(type == name);
+    } else {
+      MOZ_ASSERT(type != name);
+    }
+  #endif
   slots->mCustomElementData = aData;
 }
 
diff --git a/dom/base/nsContentUtils.cpp b/dom/base/nsContentUtils.cpp
index 81b49afea03c..437cba722ada 100644
--- a/dom/base/nsContentUtils.cpp
+++ b/dom/base/nsContentUtils.cpp
@@ -9989,9 +9989,6 @@ nsContentUtils::NewXULOrHTMLElement(Element** aResult, mozilla::dom::NodeInfo* a
              "Can only create XUL or XHTML elements.");
 
   nsAtom *name = nodeInfo->NameAtom();
-  RefPtr<nsAtom> tagAtom = nodeInfo->NameAtom();
-  RefPtr<nsAtom> typeAtom = aIs ? NS_Atomize(*aIs) : tagAtom;
-
   int32_t tag = eHTMLTag_unknown;
   bool isCustomElementName = false;
   if (nodeInfo->NamespaceEquals(kNameSpaceID_XHTML)) {
@@ -10001,7 +9998,14 @@ nsContentUtils::NewXULOrHTMLElement(Element** aResult, mozilla::dom::NodeInfo* a
   } else {
     isCustomElementName = nsContentUtils::IsCustomElementName(name);
   }
+
+  RefPtr<nsAtom> tagAtom = nodeInfo->NameAtom();
+  RefPtr<nsAtom> typeAtom;
   bool isCustomElement = isCustomElementName || aIs;
+  if (isCustomElement) {
+    typeAtom = isCustomElementName ? tagAtom : NS_Atomize(*aIs);
+  }
+
   MOZ_ASSERT_IF(aDefinition, isCustomElement);
 
   // https://dom.spec.whatwg.org/#concept-create-element
diff --git a/dom/base/nsNodeUtils.cpp b/dom/base/nsNodeUtils.cpp
index 86e31172e748..8dfa76ae0a36 100644
--- a/dom/base/nsNodeUtils.cpp
+++ b/dom/base/nsNodeUtils.cpp
@@ -504,7 +504,13 @@ nsNodeUtils::CloneAndAdopt(nsINode *aNode, bool aClone, bool aDeep,
         cloneElem->GetAttr(kNameSpaceID_None, nsGkAtoms::is, extension);
       }
 
-      if (data || !extension.IsEmpty()) {
+      if ((data && data->GetCustomElementType() == tagAtom) ||
+          !extension.IsEmpty()) {
+        // The typeAtom can be determined by extension, because we only need to
+        // consider two cases: 1) Original node is a autonomous custom element
+        // which has CustomElementData. 2) Original node is a built-in custom
+        // element or normal element, but it has `is` attribute when it is being
+        // cloned.
         RefPtr<nsAtom> typeAtom = extension.IsEmpty() ? tagAtom : NS_Atomize(extension);
         cloneElem->SetCustomElementData(new CustomElementData(typeAtom));
         CustomElementDefinition* definition =
diff --git a/parser/html/nsHtml5TreeOperation.cpp b/parser/html/nsHtml5TreeOperation.cpp
index 0444590f6c28..770d785a6922 100644
--- a/parser/html/nsHtml5TreeOperation.cpp
+++ b/parser/html/nsHtml5TreeOperation.cpp
@@ -409,7 +409,7 @@ nsHtml5TreeOperation::CreateHTMLElement(
     if (isCustomElement && aFromParser != dom::FROM_PARSER_FRAGMENT) {
       RefPtr<nsAtom> tagAtom = nodeInfo->NameAtom();
       RefPtr<nsAtom> typeAtom =
-        isValue.IsEmpty() ? tagAtom : NS_Atomize(isValue);
+        (aCreator == NS_NewCustomElement) ? tagAtom : NS_Atomize(isValue);
 
       definition = nsContentUtils::LookupCustomElementDefinition(document,
         nodeInfo->LocalName(), nodeInfo->NamespaceID(), typeAtom);
diff --git a/testing/web-platform/meta/MANIFEST.json b/testing/web-platform/meta/MANIFEST.json
index 82d5f7d42551..eb420a486330 100644
--- a/testing/web-platform/meta/MANIFEST.json
+++ b/testing/web-platform/meta/MANIFEST.json
@@ -305751,6 +305751,12 @@
      {}
     ]
    ],
+   "custom-elements/parser/parser-constructs-custom-elements-with-is.html": [
+    [
+     "/custom-elements/parser/parser-constructs-custom-elements-with-is.html",
+     {}
+    ]
+   ],
    "custom-elements/parser/parser-constructs-custom-elements.html": [
     [
      "/custom-elements/parser/parser-constructs-custom-elements.html",
@@ -523823,7 +523829,7 @@
    "testharness"
   ],
   "custom-elements/Document-createElement.html": [
-   "074c9f703cc7feb1dfc3d07aedd08460bd591d42",
+   "fb10e851deb193aed700c8ab6790c216766cc362",
    "testharness"
   ],
   "custom-elements/HTMLElement-constructor.html": [
@@ -523882,6 +523888,10 @@
    "dc0ca4a066d9a05362a81b263594965763919e46",
    "testharness"
   ],
+  "custom-elements/parser/parser-constructs-custom-elements-with-is.html": [
+   "7a7df7aab092906b5a753c0d122b971aff01517a",
+   "testharness"
+  ],
   "custom-elements/parser/parser-constructs-custom-elements.html": [
    "228d4a90d57dc942692becc6f126ec9130b3a4e0",
    "testharness"
@@ -524027,7 +524037,7 @@
    "testharness"
   ],
   "custom-elements/upgrading/Node-cloneNode.html": [
-   "cc121ea56de1b8e1074062b5dda69f57e2add665",
+   "264a2631a79370bce8392657ba52c8b0c949b7e1",
    "testharness"
   ],
   "custom-elements/upgrading/upgrading-enqueue-reactions.html": [
diff --git a/testing/web-platform/tests/custom-elements/Document-createElement.html b/testing/web-platform/tests/custom-elements/Document-createElement.html
index e446c507ca86..52a68e8e1789 100644
--- a/testing/web-platform/tests/custom-elements/Document-createElement.html
+++ b/testing/web-platform/tests/custom-elements/Document-createElement.html
@@ -29,6 +29,21 @@ test(function () {
 
 }, 'document.createElement must create an instance of custom elements');
 
+test(function () {
+    class AutonomousCustomElement extends HTMLElement {};
+    class IsCustomElement extends HTMLElement {};
+
+    customElements.define('autonomous-custom-element', AutonomousCustomElement);
+    customElements.define('is-custom-element', IsCustomElement);
+
+    var instance = document.createElement('autonomous-custom-element', { is: "is-custom-element"});
+
+    assert_true(instance instanceof AutonomousCustomElement);
+    assert_equals(instance.localName, 'autonomous-custom-element');
+    assert_equals(instance.namespaceURI, 'http://www.w3.org/1999/xhtml', 'A custom element HTML must use HTML namespace');
+
+}, 'document.createElement must create an instance of autonomous custom elements when it has is attribute');
+
 function assert_reports(expected, testFunction, message) {
     var uncaughtError = null;
     window.onerror = function (message, url, lineNumber, columnNumber, error) { uncaughtError = error; return true; }
diff --git a/testing/web-platform/tests/custom-elements/parser/parser-constructs-custom-elements-with-is.html b/testing/web-platform/tests/custom-elements/parser/parser-constructs-custom-elements-with-is.html
new file mode 100644
index 000000000000..96c00278a3d7
--- /dev/null
+++ b/testing/web-platform/tests/custom-elements/parser/parser-constructs-custom-elements-with-is.html
@@ -0,0 +1,51 @@
+<!DOCTYPE html>
+<html>
+<head>
+<title>Custom Elements: Changes to the HTML parser</title>
+<meta name="author" title="John Dai" href="mailto:jdai@mozilla.com">
+<meta name="assert" content="HTML parser creates a custom element which contains is attribute">
+<link rel="help" href="https://html.spec.whatwg.org/#create-an-element-for-the-token">
+<link rel="help" href="https://dom.spec.whatwg.org/#concept-create-element">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+</head>
+<body>
+<div id="log"></div>
+<autonomous-custom-element id="instance1" is="is-custom-element"></autonomous-custom-element>
+<script>
+
+class AutonomousCustomElement extends HTMLElement { };
+class IsCustomElement extends HTMLElement { };
+
+customElements.define('autonomous-custom-element', AutonomousCustomElement);
+customElements.define('is-custom-element', IsCustomElement);
+
+test(function () {
+    var customElement = document.getElementById('instance1');
+
+    assert_true(customElement instanceof HTMLElement, 'A resolved custom element must be an instance of HTMLElement');
+    assert_false(customElement instanceof HTMLUnknownElement, 'A resolved custom element must NOT be an instance of HTMLUnknownElement');
+    assert_true(customElement instanceof AutonomousCustomElement, 'A resolved custom element must be an instance of that custom element');
+    assert_equals(customElement.localName, 'autonomous-custom-element');
+    assert_equals(customElement.namespaceURI, 'http://www.w3.org/1999/xhtml', 'A custom element HTML must use HTML namespace');
+
+}, 'HTML parser must create a defined autonomous custom element when customElements.define comes after HTML parser creation');
+
+</script>
+<autonomous-custom-element id="instance2" is="is-custom-element"></autonomous-custom-element>
+<script>
+
+test(function () {
+    var customElement = document.getElementById('instance2');
+
+    assert_true(customElement instanceof HTMLElement, 'A resolved custom element must be an instance of HTMLElement');
+    assert_false(customElement instanceof HTMLUnknownElement, 'A resolved custom element must NOT be an instance of HTMLUnknownElement');
+    assert_true(customElement instanceof AutonomousCustomElement, 'A resolved custom element must be an instance of that custom element');
+    assert_equals(customElement.localName, 'autonomous-custom-element');
+    assert_equals(customElement.namespaceURI, 'http://www.w3.org/1999/xhtml', 'A custom element HTML must use HTML namespace');
+
+}, 'HTML parser must create a defined autonomous custom element when customElements.define comes before HTML parser creation');
+
+</script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/custom-elements/upgrading/Node-cloneNode.html b/testing/web-platform/tests/custom-elements/upgrading/Node-cloneNode.html
index 0d158fd59e48..0492e1f39a13 100644
--- a/testing/web-platform/tests/custom-elements/upgrading/Node-cloneNode.html
+++ b/testing/web-platform/tests/custom-elements/upgrading/Node-cloneNode.html
@@ -30,6 +30,25 @@ test(function () {
         'A cloned custom element must be an instance of the custom element');
 }, 'Node.prototype.cloneNode(false) must be able to clone a custom element');
 
+test(function () {
+    class AutonomousCustomElement extends HTMLElement {};
+    class IsCustomElement extends HTMLElement {};
+
+    customElements.define('autonomous-custom-element', AutonomousCustomElement);
+    customElements.define('is-custom-element', IsCustomElement);
+
+    var instance = document.createElement('autonomous-custom-element', { is: "is-custom-element"});
+    assert_true(instance instanceof HTMLElement);
+    assert_true(instance instanceof AutonomousCustomElement);
+
+    var clone = instance.cloneNode(false);
+    assert_not_equals(instance, clone);
+    assert_true(clone instanceof HTMLElement,
+        'A cloned custom element must be an instance of HTMLElement');
+    assert_true(clone instanceof AutonomousCustomElement,
+        'A cloned custom element must be an instance of the custom element');
+}, 'Node.prototype.cloneNode(false) must be able to clone as a autonomous custom element when it contains is attribute');
+
 test_with_window(function (contentWindow) {
     var contentDocument = contentWindow.document;
     class MyCustomElement extends contentWindow.HTMLElement {}