--- a/dom/base/Element.cpp
+++ b/dom/base/Element.cpp
@@ -987,31 +987,35 @@ Element::CreateShadowRoot(ErrorResult& a
   protoBinding->SetInheritsStyle(false);
 
   // Calling SetPrototypeBinding takes ownership of protoBinding.
   docInfo->SetPrototypeBinding(NS_LITERAL_CSTRING("shadowroot"), protoBinding);
 
   nsRefPtr<ShadowRoot> shadowRoot = new ShadowRoot(this, nodeInfo.forget(),
                                                    protoBinding);
 
+  shadowRoot->SetIsComposedDocParticipant(IsInComposedDoc());
+
   // Replace the old ShadowRoot with the new one and let the old
   // ShadowRoot know about the younger ShadowRoot because the old
   // ShadowRoot is projected into the younger ShadowRoot's shadow
   // insertion point (if it exists).
   ShadowRoot* olderShadow = GetShadowRoot();
   SetShadowRoot(shadowRoot);
   if (olderShadow) {
     olderShadow->SetYoungerShadow(shadowRoot);
 
     // Unbind children of older shadow root because they
     // are no longer in the composed tree.
     for (nsIContent* child = olderShadow->GetFirstChild(); child;
          child = child->GetNextSibling()) {
       child->UnbindFromTree(true, false);
     }
+
+    olderShadow->SetIsComposedDocParticipant(false);
   }
 
   // xblBinding takes ownership of docInfo.
   nsRefPtr<nsXBLBinding> xblBinding = new nsXBLBinding(shadowRoot, protoBinding);
   shadowRoot->SetAssociatedBinding(xblBinding);
   xblBinding->SetBoundElement(this);
 
   SetXBLBinding(xblBinding);
@@ -1573,16 +1577,17 @@ Element::BindToTree(nsIDocument* aDocume
     if (sheet) {
       mAttrsAndChildren.SetMappedAttrStyleSheet(sheet);
     }
   }
 
   // Call BindToTree on shadow root children.
   ShadowRoot* shadowRoot = GetShadowRoot();
   if (shadowRoot) {
+    shadowRoot->SetIsComposedDocParticipant(IsInComposedDoc());
     for (nsIContent* child = shadowRoot->GetFirstChild(); child;
          child = child->GetNextSibling()) {
       rv = child->BindToTree(nullptr, shadowRoot,
                              shadowRoot->GetBindingParent(),
                              aCompileEventHandlers);
       NS_ENSURE_SUCCESS(rv, rv);
     }
   }
@@ -1630,18 +1635,17 @@ Element::UnbindFromTree(bool aDeep, bool
   NS_PRECONDITION(aDeep || (!GetUncomposedDoc() && !GetBindingParent()),
                   "Shallow unbind won't clear document and binding parent on "
                   "kids!");
 
   RemoveFromIdTable();
 
   // Make sure to unbind this node before doing the kids
   nsIDocument* document =
-    HasFlag(NODE_FORCE_XBL_BINDINGS) || IsInShadowTree() ?
-      OwnerDoc() : GetUncomposedDoc();
+    HasFlag(NODE_FORCE_XBL_BINDINGS) ? OwnerDoc() : GetComposedDoc();
 
   if (aNullParent) {
     if (IsFullScreenAncestor()) {
       // The element being removed is an ancestor of the full-screen element,
       // exit full-screen state.
       nsContentUtils::ReportToConsole(nsIScriptError::warningFlag,
                                       NS_LITERAL_CSTRING("DOM"), OwnerDoc(),
                                       nsContentUtils::eDOM_PROPERTIES,
@@ -1751,16 +1755,18 @@ Element::UnbindFromTree(bool aDeep, bool
 
   // Unbind children of shadow root.
   ShadowRoot* shadowRoot = GetShadowRoot();
   if (shadowRoot) {
     for (nsIContent* child = shadowRoot->GetFirstChild(); child;
          child = child->GetNextSibling()) {
       child->UnbindFromTree(true, false);
     }
+
+    shadowRoot->SetIsComposedDocParticipant(false);
   }
 }
 
 nsICSSDeclaration*
 Element::GetSMILOverrideStyle()
 {
   Element::nsDOMSlots *slots = DOMSlots();
 

--- a/dom/base/ShadowRoot.cpp
+++ b/dom/base/ShadowRoot.cpp
@@ -62,17 +62,17 @@ NS_INTERFACE_MAP_END_INHERITING(Document
 NS_IMPL_ADDREF_INHERITED(ShadowRoot, DocumentFragment)
 NS_IMPL_RELEASE_INHERITED(ShadowRoot, DocumentFragment)
 
 ShadowRoot::ShadowRoot(nsIContent* aContent,
                        already_AddRefed<mozilla::dom::NodeInfo>&& aNodeInfo,
                        nsXBLPrototypeBinding* aProtoBinding)
   : DocumentFragment(aNodeInfo), mPoolHost(aContent),
     mProtoBinding(aProtoBinding), mShadowElement(nullptr),
-    mInsertionPointChanged(false)
+    mInsertionPointChanged(false), mIsComposedDocParticipant(false)
 {
   SetHost(aContent);
 
   // Nodes in a shadow tree should never store a value
   // in the subtree root pointer, nodes in the shadow tree
   // track the subtree root using GetContainingShadow().
   ClearSubtreeRootPointer();
 

--- a/dom/base/ShadowRoot.h
+++ b/dom/base/ShadowRoot.h
@@ -122,16 +122,22 @@ public:
                            const nsAString& aLocalName);
   already_AddRefed<nsContentList>
     GetElementsByClassName(const nsAString& aClasses);
   void GetInnerHTML(nsAString& aInnerHTML);
   void SetInnerHTML(const nsAString& aInnerHTML, ErrorResult& aError);
   Element* Host();
   ShadowRoot* GetOlderShadowRoot() { return mOlderShadow; }
   void StyleSheetChanged();
+
+  bool IsComposedDocParticipant() { return mIsComposedDocParticipant; }
+  void SetIsComposedDocParticipant(bool aIsComposedDocParticipant)
+  {
+    mIsComposedDocParticipant = aIsComposedDocParticipant;
+  }
 protected:
   virtual ~ShadowRoot();
 
   // The pool host is the parent of the nodes that will be distributed
   // into the insertion points in this ShadowRoot. See |ChangeShadowRoot|.
   nsCOMPtr<nsIContent> mPoolHost;
 
   // An array of content insertion points that are a descendant of the ShadowRoot
@@ -166,16 +172,22 @@ protected:
   // this ShadowRoot was created.
   nsRefPtr<ShadowRoot> mYoungerShadow;
 
   // A boolean that indicates that an insertion point was added or removed
   // from this ShadowRoot and that the nodes need to be redistributed into
   // the insertion points. After this flag is set, nodes will be distributed
   // on the next mutation event.
   bool mInsertionPointChanged;
+
+  // Flag to indicate whether the descendants of this shadow root are part of the
+  // composed document. Ideally, we would use a node flag on nodes to
+  // mark whether it is in the composed document, but we have run out of flags
+  // so instead we track it here.
+  bool mIsComposedDocParticipant;
 };
 
 class ShadowRootStyleSheetList : public StyleSheetList
 {
 public:
   explicit ShadowRootStyleSheetList(ShadowRoot* aShadowRoot);
 
   NS_DECL_ISUPPORTS_INHERITED

--- a/dom/base/nsGenericDOMDataNode.cpp
+++ b/dom/base/nsGenericDOMDataNode.cpp
@@ -108,16 +108,20 @@ NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_
   if (slots) {
     slots->Traverse(cb);
   }
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 
 NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(nsGenericDOMDataNode)
   nsINode::Unlink(tmp);
 
+  // Clear flag here because unlinking slots will clear the
+  // containing shadow root pointer.
+  tmp->UnsetFlags(NODE_IS_IN_SHADOW_TREE);
+
   nsDataSlots *slots = tmp->GetExistingDataSlots();
   if (slots) {
     slots->Unlink();
   }
 NS_IMPL_CYCLE_COLLECTION_UNLINK_END
 
 NS_INTERFACE_MAP_BEGIN(nsGenericDOMDataNode)
   NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
@@ -557,18 +561,17 @@ nsGenericDOMDataNode::BindToTree(nsIDocu
 void
 nsGenericDOMDataNode::UnbindFromTree(bool aDeep, bool aNullParent)
 {
   // Unset frame flags; if we need them again later, they'll get set again.
   UnsetFlags(NS_CREATE_FRAME_IF_NON_WHITESPACE |
              NS_REFRAME_IF_WHITESPACE);
 
   nsIDocument* document =
-    HasFlag(NODE_FORCE_XBL_BINDINGS) || IsInShadowTree() ?
-      OwnerDoc() : GetUncomposedDoc();
+    HasFlag(NODE_FORCE_XBL_BINDINGS) ? OwnerDoc() : GetComposedDoc();
 
   if (aNullParent) {
     if (GetParent()) {
       NS_RELEASE(mParent);
     } else {
       mParent = nullptr;
     }
     SetParentIsContent(false);

--- a/dom/base/nsINode.cpp
+++ b/dom/base/nsINode.cpp
@@ -385,27 +385,18 @@ nsINode::GetTextContentInternal(nsAStrin
 }
 
 nsIDocument*
 nsINode::GetComposedDocInternal() const
 {
   MOZ_ASSERT(HasFlag(NODE_IS_IN_SHADOW_TREE) && IsContent(),
              "Should only be caled on nodes in the shadow tree.");
 
-  // Cross ShadowRoot boundary.
   ShadowRoot* containingShadow = AsContent()->GetContainingShadow();
-
-  nsIContent* poolHost = containingShadow->GetPoolHost();
-  if (!poolHost) {
-    // This node is in an older shadow root that does not get projected into
-    // an insertion point, thus this node can not be in the composed document.
-    return nullptr;
-  }
-
-  return poolHost->GetComposedDoc();
+  return containingShadow->IsComposedDocParticipant() ?  OwnerDoc() : nullptr;
 }
 
 #ifdef DEBUG
 void
 nsINode::CheckNotNativeAnonymous() const
 {
   if (!IsNodeOfType(eCONTENT))
     return;

--- a/dom/base/nsINode.h
+++ b/dom/base/nsINode.h
@@ -515,21 +515,19 @@ public:
    * @deprecated
    */
   nsIDocument *GetCurrentDoc() const
   {
     return GetUncomposedDoc();
   }
 
   /**
-   * This method gets the current doc of the node hosting this content
-   * or the current doc of this content if it is not being hosted. This
-   * method walks through ShadowRoot boundaries until it reach the host
-   * that is located in the root of the "tree of trees" (see Shadow DOM
-   * spec) and returns the current doc for that host.
+   * This method returns the owner doc if the node is in the
+   * composed document (as defined in the Shadow DOM spec), otherwise
+   * it returns null.
    */
   nsIDocument* GetComposedDoc() const
   {
     return IsInShadowTree() ?
       GetComposedDocInternal() : GetUncomposedDoc();
   }
 
   /**

--- a/dom/html/HTMLShadowElement.cpp
+++ b/dom/html/HTMLShadowElement.cpp
@@ -141,16 +141,18 @@ HTMLShadowElement::BindToTree(nsIDocumen
 
     containingShadow->SetInsertionPointChanged();
   }
 
   if (mIsInsertionPoint && containingShadow) {
     // Propagate BindToTree calls to projected shadow root children.
     ShadowRoot* projectedShadow = containingShadow->GetOlderShadowRoot();
     if (projectedShadow) {
+      projectedShadow->SetIsComposedDocParticipant(IsInComposedDoc());
+
       for (nsIContent* child = projectedShadow->GetFirstChild(); child;
            child = child->GetNextSibling()) {
         rv = child->BindToTree(nullptr, projectedShadow,
                                projectedShadow->GetBindingParent(),
                                aCompileEventHandlers);
         NS_ENSURE_SUCCESS(rv, rv);
       }
     }
@@ -168,16 +170,18 @@ HTMLShadowElement::UnbindFromTree(bool a
     // Propagate UnbindFromTree call to previous projected shadow
     // root children.
     ShadowRoot* projectedShadow = oldContainingShadow->GetOlderShadowRoot();
     if (projectedShadow) {
       for (nsIContent* child = projectedShadow->GetFirstChild(); child;
            child = child->GetNextSibling()) {
         child->UnbindFromTree(true, false);
       }
+
+      projectedShadow->SetIsComposedDocParticipant(false);
     }
   }
 
   nsGenericHTMLElement::UnbindFromTree(aDeep, aNullParent);
 
   if (oldContainingShadow && !GetContainingShadow() && mIsInsertionPoint) {
     nsTArray<HTMLShadowElement*>& shadowDescendants =
       oldContainingShadow->ShadowDescendants();

--- a/dom/html/HTMLStyleElement.cpp
+++ b/dom/html/HTMLStyleElement.cpp
@@ -152,25 +152,24 @@ HTMLStyleElement::BindToTree(nsIDocument
 
   return rv;  
 }
 
 void
 HTMLStyleElement::UnbindFromTree(bool aDeep, bool aNullParent)
 {
   nsCOMPtr<nsIDocument> oldDoc = GetUncomposedDoc();
-  nsCOMPtr<nsIDocument> oldComposedDoc = GetComposedDoc();
   ShadowRoot* oldShadow = GetContainingShadow();
 
   nsGenericHTMLElement::UnbindFromTree(aDeep, aNullParent);
 
-  if (GetContainingShadow() && !oldComposedDoc) {
-    // The style is in a shadow tree and was already not
-    // in the composed document. Thus the sheet does not
-    // need to be updated.
+  if (oldShadow && GetContainingShadow()) {
+    // The style is in a shadow tree and is still in the
+    // shadow tree. Thus the sheets in the shadow DOM
+    // do not need to be updated.
     return;
   }
 
   UpdateStyleSheetInternal(oldDoc, oldShadow);
 }
 
 nsresult
 HTMLStyleElement::SetAttr(int32_t aNameSpaceID, nsIAtom* aName,