--- a/dom/base/ChildIterator.cpp
+++ b/dom/base/ChildIterator.cpp
@@ -7,16 +7,17 @@
 #include "ChildIterator.h"
 #include "nsContentUtils.h"
 #include "mozilla/dom/HTMLSlotElement.h"
 #include "mozilla/dom/XBLChildrenElement.h"
 #include "mozilla/dom/ShadowRoot.h"
 #include "nsIAnonymousContentCreator.h"
 #include "nsIFrame.h"
 #include "nsCSSAnonBoxes.h"
+#include "nsDocument.h"
 
 namespace mozilla {
 namespace dom {
 
 class MatchedNodes {
 public:
   explicit MatchedNodes()
     : mIsContentElement(false), mChildrenElement(nullptr) {}
@@ -61,17 +62,17 @@ GetMatchedNodesForPoint(nsIContent* aCon
 ExplicitChildIterator::ExplicitChildIterator(const nsIContent* aParent,
                                              bool aStartAtBeginning)
   : mParent(aParent),
     mChild(nullptr),
     mDefaultChild(nullptr),
     mIsFirst(aStartAtBeginning),
     mIndexInInserted(0)
 {
-  mParentAsSlot = nsContentUtils::IsWebComponentsEnabled() ?
+  mParentAsSlot = nsDocument::IsWebComponentsEnabled(mParent) ?
     HTMLSlotElement::FromContent(mParent) : nullptr;
 }
 
 nsIContent*
 ExplicitChildIterator::GetNextChild()
 {
   // If we're already in the inserted-children array, look there first
   if (mIndexInInserted) {

--- a/dom/base/nsContentUtils.cpp
+++ b/dom/base/nsContentUtils.cpp
@@ -7529,17 +7529,17 @@ nsContentUtils::IsContentInsertionPoint(
   // XXX handle <slot>?
   return false;
 }
 
 // static
 bool
 nsContentUtils::HasDistributedChildren(nsIContent* aContent)
 {
-  if (!IsWebComponentsEnabled() || !aContent) {
+  if (!aContent || !nsDocument::IsWebComponentsEnabled(aContent)) {
     return false;
   }
 
   if (aContent->GetShadowRoot()) {
     // Children of a shadow root host are distributed
     // to content insertion points in the shadow root.
     return true;
   }

--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -1533,16 +1533,17 @@ nsIDocument::nsIDocument()
     mHasScrollLinkedEffect(false),
     mFrameRequestCallbacksScheduled(false),
     mIsTopLevelContentDocument(false),
     mIsContentDocument(false),
     mDidCallBeginLoad(false),
     mBufferingCSPViolations(false),
     mAllowPaymentRequest(false),
     mEncodingMenuDisabled(false),
+    mIsWebComponentsEnabled(false),
     mIsScopedStyleEnabled(eScopedStyle_Unknown),
     mCompatMode(eCompatibility_FullStandards),
     mReadyState(ReadyState::READYSTATE_UNINITIALIZED),
     mStyleBackendType(StyleBackendType::None),
 #ifdef MOZILLA_INTERNAL_API
     mVisibilityState(dom::VisibilityState::Hidden),
 #else
     mDummy(0),
@@ -2715,16 +2716,58 @@ nsDocument::IsSynthesized() {
   bool synthesized = false;
   if (internalChan) {
     DebugOnly<nsresult> rv = internalChan->GetResponseSynthesized(&synthesized);
     MOZ_ASSERT(NS_SUCCEEDED(rv), "GetResponseSynthesized shouldn't fail.");
   }
   return synthesized;
 }
 
+bool
+nsDocument::IsWebComponentsEnabled(JSContext* aCx, JSObject* aObject)
+{
+  JS::Rooted<JSObject*> obj(aCx, aObject);
+
+  JSAutoCompartment ac(aCx, obj);
+  JS::Rooted<JSObject*> global(aCx, JS_GetGlobalForObject(aCx, obj));
+  nsCOMPtr<nsPIDOMWindowInner> window =
+    do_QueryInterface(nsJSUtils::GetStaticScriptGlobal(global));
+
+  nsIDocument* doc = window ? window->GetExtantDoc() : nullptr;
+  if (!doc) {
+    return false;
+  }
+
+  // Once it is enabled for a document, it stays enabled.
+  if (doc->IsWebComponentsEnabled()) {
+    return true;
+  }
+
+  bool enabled = nsContentUtils::IsWebComponentsEnabled();
+  doc->SetWebComponentsEnabled(enabled);
+
+  return enabled;
+}
+
+bool
+nsDocument::IsWebComponentsEnabled(const nsINode* aNode)
+{
+  nsIDocument* doc = aNode->OwnerDoc();
+
+  // Once it is enabled for a document, it stays enabled.
+  if (doc->IsWebComponentsEnabled()) {
+    return true;
+  }
+
+  bool enabled = nsContentUtils::IsWebComponentsEnabled();
+  doc->SetWebComponentsEnabled(enabled);
+
+  return enabled;
+}
+
 nsresult
 nsDocument::StartDocumentLoad(const char* aCommand, nsIChannel* aChannel,
                               nsILoadGroup* aLoadGroup,
                               nsISupports* aContainer,
                               nsIStreamListener **aDocListener,
                               bool aReset, nsIContentSink* aSink)
 {
   if (MOZ_LOG_TEST(gDocumentLeakPRLog, LogLevel::Debug)) {

--- a/dom/base/nsDocument.h
+++ b/dom/base/nsDocument.h
@@ -660,16 +660,21 @@ public:
 
   virtual void NotifyLayerManagerRecreated() override;
 
   virtual void ScheduleSVGForPresAttrEvaluation(nsSVGElement* aSVG) override;
   virtual void UnscheduleSVGForPresAttrEvaluation(nsSVGElement* aSVG) override;
   virtual void ResolveScheduledSVGPresAttrs() override;
   bool IsSynthesized();
 
+  // Check whether web components are enabled for the global of aObject.
+  static bool IsWebComponentsEnabled(JSContext* aCx, JSObject* aObject);
+  // Check whether web components are enabled for the document this node belongs
+  // to.
+  static bool IsWebComponentsEnabled(const nsINode* aNode);
 private:
   void AddOnDemandBuiltInUASheet(mozilla::StyleSheet* aSheet);
   void SendToConsole(nsCOMArray<nsISecurityConsoleMessage>& aMessages);
 
 public:
   // nsIDOMNode
   NS_FORWARD_NSIDOMNODE_TO_NSINODE_OVERRIDABLE
 

--- a/dom/base/nsIDocument.h
+++ b/dom/base/nsIDocument.h
@@ -3251,16 +3251,26 @@ public:
   {
     MOZ_ASSERT(mIgnoreOpensDuringUnloadCounter);
     --mIgnoreOpensDuringUnloadCounter;
   }
 
   virtual bool AllowPaymentRequest() const = 0;
   virtual void SetAllowPaymentRequest(bool aAllowPaymentRequest) = 0;
 
+  bool IsWebComponentsEnabled() const
+  {
+    return mIsWebComponentsEnabled;
+  }
+
+  void SetWebComponentsEnabled(bool aEnabled)
+  {
+    mIsWebComponentsEnabled = aEnabled;
+  }
+
 protected:
   bool GetUseCounter(mozilla::UseCounter aUseCounter)
   {
     return mUseCounters[aUseCounter];
   }
 
   void SetChildDocumentUseCounter(mozilla::UseCounter aUseCounter)
   {
@@ -3607,16 +3617,20 @@ protected:
   bool mBufferingCSPViolations : 1;
 
   // True if the document is allowed to use PaymentRequest.
   bool mAllowPaymentRequest : 1;
 
   // True if the encoding menu should be disabled.
   bool mEncodingMenuDisabled : 1;
 
+  // True if dom.webcomponents.enabled pref is set. It can not be unset once
+  // set to true.
+  bool mIsWebComponentsEnabled : 1;
+
   // Whether <style scoped> support is enabled in this document.
   enum { eScopedStyle_Unknown, eScopedStyle_Disabled, eScopedStyle_Enabled };
   unsigned int mIsScopedStyleEnabled : 2;
 
   // Compatibility mode
   nsCompatibility mCompatMode;
 
   // Our readyState

--- a/dom/base/nsTextNode.cpp
+++ b/dom/base/nsTextNode.cpp
@@ -16,16 +16,17 @@
 #include "nsIDOMMutationEvent.h"
 #include "nsIDocument.h"
 #include "nsThreadUtils.h"
 #include "nsStubMutationObserver.h"
 #include "mozilla/IntegerPrintfMacros.h"
 #ifdef DEBUG
 #include "nsRange.h"
 #endif
+#include "nsDocument.h"
 
 using namespace mozilla;
 using namespace mozilla::dom;
 
 /**
  * class used to implement attr() generated content
  */
 class nsAttributeTextNode final : public nsTextNode,
@@ -152,16 +153,22 @@ nsTextNode::BindToTree(nsIDocument* aDoc
 
 void nsTextNode::UnbindFromTree(bool aDeep, bool aNullParent)
 {
   ResetDirectionSetByTextNode(this);
 
   nsGenericDOMDataNode::UnbindFromTree(aDeep, aNullParent);
 }
 
+bool
+nsTextNode::IsWebComponentsEnabled(JSContext* aCx, JSObject* aObject)
+{
+  return nsDocument::IsWebComponentsEnabled(aCx, aObject);
+}
+
 #ifdef DEBUG
 void
 nsTextNode::List(FILE* out, int32_t aIndent) const
 {
   int32_t index;
   for (index = aIndent; --index >= 0; ) fputs("  ", out);
 
   fprintf(out, "Text@%p", static_cast<const void*>(this));

--- a/dom/base/nsTextNode.h
+++ b/dom/base/nsTextNode.h
@@ -70,16 +70,20 @@ public:
   virtual void UnbindFromTree(bool aDeep = true,
                               bool aNullParent = true) override;
 
   nsresult AppendTextForNormalize(const char16_t* aBuffer, uint32_t aLength,
                                   bool aNotify, nsIContent* aNextSibling);
 
   virtual nsIDOMNode* AsDOMNode() override { return this; }
 
+  // Need to have a copy here because including nsDocument.h in this file will
+  // fail to build on Windows.
+  static bool IsWebComponentsEnabled(JSContext* aCx, JSObject* aObject);
+
 #ifdef DEBUG
   virtual void List(FILE* out, int32_t aIndent) const override;
   virtual void DumpContent(FILE* out, int32_t aIndent, bool aDumpAll) const override;
 #endif
 
 protected:
   virtual ~nsTextNode();
 

--- a/dom/html/HTMLSlotElement.cpp
+++ b/dom/html/HTMLSlotElement.cpp
@@ -11,17 +11,17 @@
 #include "nsGkAtoms.h"
 #include "nsDocument.h"
 
 nsGenericHTMLElement*
 NS_NewHTMLSlotElement(already_AddRefed<mozilla::dom::NodeInfo>&& aNodeInfo,
                       mozilla::dom::FromParser aFromParser)
 {
   RefPtr<mozilla::dom::NodeInfo> nodeInfo(aNodeInfo);
-  if (nsContentUtils::IsWebComponentsEnabled()) {
+  if (nsDocument::IsWebComponentsEnabled(nodeInfo->GetDocument())) {
     already_AddRefed<mozilla::dom::NodeInfo> nodeInfoArg(nodeInfo.forget());
     return new mozilla::dom::HTMLSlotElement(nodeInfoArg);
   }
 
   already_AddRefed<mozilla::dom::NodeInfo> nodeInfoArg(nodeInfo.forget());
   return new mozilla::dom::HTMLUnknownElement(nodeInfoArg);
 }
 

--- a/dom/webidl/Element.webidl
+++ b/dom/webidl/Element.webidl
@@ -240,29 +240,29 @@ partial interface Element {
 // https://dom.spec.whatwg.org/#dictdef-shadowrootinit
 dictionary ShadowRootInit {
   required ShadowRootMode mode;
 };
 
 // https://dom.spec.whatwg.org/#element
 partial interface Element {
   // Shadow DOM v1
-  [Throws, Pref="dom.webcomponents.enabled"]
+  [Throws, Func="nsDocument::IsWebComponentsEnabled"]
   ShadowRoot attachShadow(ShadowRootInit shadowRootInitDict);
-  [BinaryName="shadowRootByMode", Pref="dom.webcomponents.enabled"]
+  [BinaryName="shadowRootByMode", Func="nsDocument::IsWebComponentsEnabled"]
   readonly attribute ShadowRoot? shadowRoot;
-  [BinaryName="assignedSlotByMode", Pref="dom.webcomponents.enabled"]
+  [BinaryName="assignedSlotByMode", Func="nsDocument::IsWebComponentsEnabled"]
   readonly attribute HTMLSlotElement? assignedSlot;
-  [CEReactions, Unscopable, SetterThrows, Pref="dom.webcomponents.enabled"]
+  [CEReactions, Unscopable, SetterThrows, Func="nsDocument::IsWebComponentsEnabled"]
            attribute DOMString slot;
 
   // [deprecated] Shadow DOM v0
-  [Throws, Pref="dom.webcomponents.enabled"]
+  [Throws, Func="nsDocument::IsWebComponentsEnabled"]
   ShadowRoot createShadowRoot();
-  [Pref="dom.webcomponents.enabled"]
+  [Func="nsDocument::IsWebComponentsEnabled"]
   NodeList getDestinationInsertionPoints();
 };
 
 Element implements ChildNode;
 Element implements NonDocumentTypeChildNode;
 Element implements ParentNode;
 Element implements Animatable;
 Element implements GeometryUtils;

--- a/dom/webidl/HTMLSlotElement.webidl
+++ b/dom/webidl/HTMLSlotElement.webidl
@@ -6,17 +6,17 @@
  * The origin of this IDL file is
  * https://html.spec.whatwg.org/multipage/forms.html#the-dialog-element
  *
  * © Copyright 2004-2011 Apple Computer, Inc., Mozilla Foundation, and
  * Opera Software ASA. You are granted a license to use, reproduce
  * and create derivative works of this document.
  */
 
-[Pref="dom.webcomponents.enabled", Exposed=Window, HTMLConstructor]
+[Func="nsDocument::IsWebComponentsEnabled", Exposed=Window, HTMLConstructor]
 interface HTMLSlotElement : HTMLElement {
   [CEReactions, SetterThrows] attribute DOMString name;
   sequence<Node> assignedNodes(optional AssignedNodesOptions options);
 };
 
 dictionary AssignedNodesOptions {
   boolean flatten = false;
 };

--- a/dom/webidl/ShadowRoot.webidl
+++ b/dom/webidl/ShadowRoot.webidl
@@ -12,17 +12,17 @@
 
 // https://dom.spec.whatwg.org/#enumdef-shadowrootmode
 enum ShadowRootMode {
   "open",
   "closed"
 };
 
 // https://dom.spec.whatwg.org/#shadowroot
-[Pref="dom.webcomponents.enabled"]
+[Func="nsDocument::IsWebComponentsEnabled"]
 interface ShadowRoot : DocumentFragment
 {
   // Shadow DOM v1
   readonly attribute ShadowRootMode mode;
   readonly attribute Element host;
 
   // [deprecated] Shadow DOM v0
   Element? getElementById(DOMString elementId);

--- a/dom/webidl/Text.webidl
+++ b/dom/webidl/Text.webidl
@@ -14,13 +14,13 @@
 interface Text : CharacterData {
   [Throws]
   Text splitText(unsigned long offset);
   [Throws]
   readonly attribute DOMString wholeText;
 };
 
 partial interface Text {
-  [BinaryName="assignedSlotByMode", Pref="dom.webcomponents.enabled"]
+  [BinaryName="assignedSlotByMode", Func="nsTextNode::IsWebComponentsEnabled"]
   readonly attribute HTMLSlotElement? assignedSlot;
 };
 
 Text implements GeometryUtils;