diff --git a/layout/style/StyleRule.cpp b/layout/style/StyleRule.cpp
index 13641915b59c..eb79dd8c216a 100644
--- a/layout/style/StyleRule.cpp
+++ b/layout/style/StyleRule.cpp
@@ -20,6 +20,7 @@
 #include "nsIAtom.h"
 #include "nsString.h"
 #include "nsStyleUtil.h"
+#include "nsICSSStyleRuleDOMWrapper.h"
 #include "nsDOMCSSDeclaration.h"
 #include "nsNameSpaceManager.h"
 #include "nsXMLNameSpaceMap.h"
@@ -1046,26 +1047,30 @@ nsCSSSelectorList::SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) cons
 
 // --------------------------------------------------------
 
+namespace mozilla {
+namespace css {
+class DOMCSSStyleRule;
+} // namespace css
+} // namespace mozilla
+
 class DOMCSSDeclarationImpl : public nsDOMCSSDeclaration
 {
 protected:
-  // Needs to be protected so we can use NS_IMPL_ADDREF_USING_AGGREGATOR.
   virtual ~DOMCSSDeclarationImpl(void);
 
-  // But we need to allow UniquePtr to delete us.
-  friend class mozilla::DefaultDelete<DOMCSSDeclarationImpl>;
-
 public:
   explicit DOMCSSDeclarationImpl(css::StyleRule *aRule);
 
   NS_IMETHOD GetParentRule(nsIDOMCSSRule **aParent) override;
+  void DropReference(void);
   virtual DeclarationBlock* GetCSSDeclaration(Operation aOperation) override;
   virtual nsresult SetCSSDeclaration(DeclarationBlock* aDecl) override;
   virtual void GetCSSParsingEnvironment(CSSParsingEnvironment& aCSSParseEnv) override;
   virtual nsIDocument* DocToUpdate() override;
 
-  // Override |AddRef| and |Release| for being owned by StyleRule.  Also, we
-  // need to forward QI for cycle collection things to StyleRule.
+  // Override |AddRef| and |Release| for being a member of
+  // |DOMCSSStyleRule|.  Also, we need to forward QI for cycle
+  // collection things to DOMCSSStyleRule.
   NS_DECL_ISUPPORTS_INHERITED
 
   virtual nsINode *GetParentObject() override
@@ -1073,12 +1078,55 @@ public:
     return mRule ? mRule->GetDocument() : nullptr;
   }
 
+  friend class css::DOMCSSStyleRule;
+
 protected:
-  // This reference is not reference-counted. The rule object owns us and we go
-  // away when it does.
+  // This reference is not reference-counted. The rule object tells us
+  // when it's about to go away.
   css::StyleRule *mRule;
+
+  inline css::DOMCSSStyleRule* DomRule();
+
+private:
+  // NOT TO BE IMPLEMENTED
+  // This object cannot be allocated on its own.  It must be a member of
+  // DOMCSSStyleRule.
+  void* operator new(size_t size) CPP_THROW_NEW;
 };
 
+namespace mozilla {
+namespace css {
+
+class DOMCSSStyleRule : public nsICSSStyleRuleDOMWrapper
+{
+public:
+  explicit DOMCSSStyleRule(StyleRule *aRule);
+
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(DOMCSSStyleRule)
+  NS_DECL_NSIDOMCSSRULE
+  NS_DECL_NSIDOMCSSSTYLERULE
+
+  // nsICSSStyleRuleDOMWrapper
+  NS_IMETHOD GetCSSStyleRule(StyleRule **aResult) override;
+
+  DOMCSSDeclarationImpl* DOMDeclaration() { return &mDOMDeclaration; }
+
+  friend class ::DOMCSSDeclarationImpl;
+
+protected:
+  virtual ~DOMCSSStyleRule();
+
+  DOMCSSDeclarationImpl mDOMDeclaration;
+
+  StyleRule* Rule() {
+    return mDOMDeclaration.mRule;
+  }
+};
+
+} // namespace css
+} // namespace mozilla
+
 DOMCSSDeclarationImpl::DOMCSSDeclarationImpl(css::StyleRule *aRule)
   : mRule(aRule)
 {
@@ -1086,32 +1134,50 @@ DOMCSSDeclarationImpl::DOMCSSDeclarationImpl(css::StyleRule *aRule)
 
 DOMCSSDeclarationImpl::~DOMCSSDeclarationImpl(void)
 {
+  NS_ASSERTION(!mRule, "DropReference not called.");
 }
 
-NS_IMPL_ADDREF_USING_AGGREGATOR(DOMCSSDeclarationImpl, mRule)
-NS_IMPL_RELEASE_USING_AGGREGATOR(DOMCSSDeclarationImpl, mRule)
+inline css::DOMCSSStyleRule* DOMCSSDeclarationImpl::DomRule()
+{
+  return reinterpret_cast<css::DOMCSSStyleRule*>
+                         (reinterpret_cast<char*>(this) -
+           offsetof(css::DOMCSSStyleRule, mDOMDeclaration));
+}
+
+NS_IMPL_ADDREF_USING_AGGREGATOR(DOMCSSDeclarationImpl, DomRule())
+NS_IMPL_RELEASE_USING_AGGREGATOR(DOMCSSDeclarationImpl, DomRule())
 
 NS_INTERFACE_MAP_BEGIN(DOMCSSDeclarationImpl)
   NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
-  // We forward the cycle collection interfaces to mRule, which is
-  // never null.
+  // We forward the cycle collection interfaces to DomRule(), which is
+  // never null (in fact, we're part of that object!)
   if (aIID.Equals(NS_GET_IID(nsCycleCollectionISupports)) ||
       aIID.Equals(NS_GET_IID(nsXPCOMCycleCollectionParticipant))) {
-    return mRule->QueryInterface(aIID, aInstancePtr);
+    return DomRule()->QueryInterface(aIID, aInstancePtr);
   }
   else
 NS_IMPL_QUERY_TAIL_INHERITING(nsDOMCSSDeclaration)
 
+void
+DOMCSSDeclarationImpl::DropReference(void)
+{
+  mRule = nullptr;
+}
+
 DeclarationBlock*
 DOMCSSDeclarationImpl::GetCSSDeclaration(Operation aOperation)
 {
-  if (aOperation != eOperation_Read) {
-    RefPtr<CSSStyleSheet> sheet = mRule->GetStyleSheet();
-    if (sheet) {
-      sheet->WillDirty();
+  if (mRule) {
+    if (aOperation != eOperation_Read) {
+      RefPtr<CSSStyleSheet> sheet = mRule->GetStyleSheet();
+      if (sheet) {
+        sheet->WillDirty();
+      }
     }
+    return mRule->GetDeclaration();
+  } else {
+    return nullptr;
   }
-  return mRule->GetDeclaration();
 }
 
 void
@@ -1125,6 +1191,11 @@ DOMCSSDeclarationImpl::GetParentRule(nsIDOMCSSRule **aParent)
 {
   NS_ENSURE_ARG_POINTER(aParent);
 
+  if (!mRule) {
+    *aParent = nullptr;
+    return NS_OK;
+  }
+
   NS_IF_ADDREF(*aParent = mRule->GetDOMRule());
   return NS_OK;
 }
@@ -1161,13 +1232,50 @@ DOMCSSDeclarationImpl::DocToUpdate()
   return nullptr;
 }
 
-// -- StyleRule ------------------------------------
-
 namespace mozilla {
 namespace css {
 
+DOMCSSStyleRule::DOMCSSStyleRule(StyleRule* aRule)
+  : mDOMDeclaration(aRule)
+{
+}
+
+DOMCSSStyleRule::~DOMCSSStyleRule()
+{
+}
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(DOMCSSStyleRule)
+  NS_INTERFACE_MAP_ENTRY(nsICSSStyleRuleDOMWrapper)
+  NS_INTERFACE_MAP_ENTRY(nsIDOMCSSStyleRule)
+  NS_INTERFACE_MAP_ENTRY(nsIDOMCSSRule)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+  NS_DOM_INTERFACE_MAP_ENTRY_CLASSINFO(CSSStyleRule)
+NS_INTERFACE_MAP_END
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(DOMCSSStyleRule)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(DOMCSSStyleRule)
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(DOMCSSStyleRule)
+
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(DOMCSSStyleRule)
+  // Trace the wrapper for our declaration.  This just expands out
+  // NS_IMPL_CYCLE_COLLECTION_TRACE_PRESERVED_WRAPPER which we can't use
+  // directly because the wrapper is on the declaration, not on us.
+  tmp->DOMDeclaration()->TraceWrapper(aCallbacks, aClosure);
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(DOMCSSStyleRule)
+  // Unlink the wrapper for our declaraton.  This just expands out
+  // NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER which we can't use
+  // directly because the wrapper is on the declaration, not on us.
+  tmp->DOMDeclaration()->ReleaseWrapper(static_cast<nsISupports*>(p));
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(DOMCSSStyleRule)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
 NS_IMETHODIMP
-StyleRule::GetType(uint16_t* aType)
+DOMCSSStyleRule::GetType(uint16_t* aType)
 {
   *aType = nsIDOMCSSRule::STYLE_RULE;
   
@@ -1175,42 +1283,95 @@ StyleRule::GetType(uint16_t* aType)
 }
 
 NS_IMETHODIMP
-StyleRule::GetParentStyleSheet(nsIDOMCSSStyleSheet** aSheet)
+DOMCSSStyleRule::GetCssText(nsAString& aCssText)
 {
-  return Rule::GetParentStyleSheet(aSheet);
+  if (!Rule()) {
+    aCssText.Truncate();
+  } else {
+    Rule()->GetCssText(aCssText);
+  }
+  return NS_OK;
 }
 
 NS_IMETHODIMP
-StyleRule::GetParentRule(nsIDOMCSSRule** aParentRule)
+DOMCSSStyleRule::SetCssText(const nsAString& aCssText)
 {
-  return Rule::GetParentRule(aParentRule);
+  if (Rule()) {
+    Rule()->SetCssText(aCssText);
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+DOMCSSStyleRule::GetParentStyleSheet(nsIDOMCSSStyleSheet** aSheet)
+{
+  if (!Rule()) {
+    *aSheet = nullptr;
+    return NS_OK;
+  }
+  return Rule()->GetParentStyleSheet(aSheet);
+}
+
+NS_IMETHODIMP
+DOMCSSStyleRule::GetParentRule(nsIDOMCSSRule** aParentRule)
+{
+  if (!Rule()) {
+    *aParentRule = nullptr;
+    return NS_OK;
+  }
+  return Rule()->GetParentRule(aParentRule);
 }
 
 css::Rule*
-StyleRule::GetCSSRule()
+DOMCSSStyleRule::GetCSSRule()
 {
-  return this;
+  return Rule();
 }
 
 NS_IMETHODIMP
-StyleRule::GetStyle(nsIDOMCSSStyleDeclaration** aStyle)
+DOMCSSStyleRule::GetSelectorText(nsAString& aSelectorText)
 {
-  if (!mDOMDeclaration) {
-    mDOMDeclaration.reset(new DOMCSSDeclarationImpl(this));
+  if (!Rule()) {
+    aSelectorText.Truncate();
+  } else {
+    Rule()->GetSelectorText(aSelectorText);
   }
-  *aStyle = mDOMDeclaration.get();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+DOMCSSStyleRule::SetSelectorText(const nsAString& aSelectorText)
+{
+  if (Rule()) {
+    Rule()->SetSelectorText(aSelectorText);
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+DOMCSSStyleRule::GetStyle(nsIDOMCSSStyleDeclaration** aStyle)
+{
+  *aStyle = &mDOMDeclaration;
   NS_ADDREF(*aStyle);
   return NS_OK;
 }
 
 NS_IMETHODIMP
-StyleRule::GetCSSStyleRule(StyleRule **aResult)
+DOMCSSStyleRule::GetCSSStyleRule(StyleRule **aResult)
 {
-  *aResult = this;
-  NS_ADDREF(*aResult);
+  *aResult = Rule();
+  NS_IF_ADDREF(*aResult);
   return NS_OK;
 }
 
+} // namespace css
+} // namespace mozilla
+
+// -- StyleRule ------------------------------------
+
+namespace mozilla {
+namespace css {
+
 StyleRule::StyleRule(nsCSSSelectorList* aSelector,
                      Declaration* aDeclaration,
                      uint32_t aLineNumber,
@@ -1245,6 +1406,11 @@ StyleRule::~StyleRule()
 void
 StyleRule::DropReferences()
 {
+  if (mDOMRule) {
+    mDOMRule->DOMDeclaration()->DropReference();
+    mDOMRule = nullptr;
+  }
+
   if (mDeclaration) {
     mDeclaration->SetOwningRule(nullptr);
   }
@@ -1258,36 +1424,18 @@ NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION_INHERITED(StyleRule)
     return NS_OK;
   }
   else
-  NS_INTERFACE_MAP_ENTRY(nsICSSStyleRuleDOMWrapper)
-  NS_INTERFACE_MAP_ENTRY(nsIDOMCSSStyleRule)
-  NS_INTERFACE_MAP_ENTRY(nsIDOMCSSRule)
-  NS_DOM_INTERFACE_MAP_ENTRY_CLASSINFO(CSSStyleRule)
 NS_INTERFACE_MAP_END_INHERITING(Rule)
 
 NS_IMPL_ADDREF_INHERITED(StyleRule, Rule)
 NS_IMPL_RELEASE_INHERITED(StyleRule, Rule)
 
 NS_IMPL_CYCLE_COLLECTION_CLASS(StyleRule)
-NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN_INHERITED(StyleRule, Rule)
-  // Keep this in sync with IsCCLeaf.
-  // Trace the wrapper for our declaration.  This just expands out
-  // NS_IMPL_CYCLE_COLLECTION_TRACE_PRESERVED_WRAPPER which we can't use
-  // directly because the wrapper is on the declaration, not on us.
-  if (tmp->mDOMDeclaration) {
-    tmp->mDOMDeclaration->TraceWrapper(aCallbacks, aClosure);
-  }
-NS_IMPL_CYCLE_COLLECTION_TRACE_END
 NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(StyleRule, Rule)
-  // Unlink the wrapper for our declaraton.  This just expands out
-  // NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER which we can't use
-  // directly because the wrapper is on the declaration, not on us.
-  if (tmp->mDOMDeclaration) {
-    tmp->mDOMDeclaration->ReleaseWrapper(static_cast<nsISupports*>(p));
-  }
   tmp->DropReferences();
 NS_IMPL_CYCLE_COLLECTION_UNLINK_END
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(StyleRule, Rule)
   // Keep this in sync with IsCCLeaf.
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mDOMRule)
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 
 bool
@@ -1297,7 +1445,7 @@ StyleRule::IsCCLeaf() const
     return false;
   }
 
-  return !mDOMDeclaration || !mDOMDeclaration->PreservingWrapper();
+  return !mDOMRule || !mDOMRule->DOMDeclaration()->PreservingWrapper();
 }
 
 /* virtual */ int32_t
@@ -1316,7 +1464,16 @@ StyleRule::Clone() const
 /* virtual */ nsIDOMCSSRule*
 StyleRule::GetDOMRule()
 {
-  return this;
+  if (!mDOMRule) {
+    if (!GetStyleSheet()) {
+      // Inline style rules aren't supposed to have a DOM rule object, only
+      // a declaration.  But if we do have one already, from a style sheet
+      // rule that used to be in a document, we still want to return it.
+      return nullptr;
+    }
+    mDOMRule = new DOMCSSStyleRule(this);
+  }
+  return mDOMRule;
 }
 
 void
@@ -1373,7 +1530,7 @@ StyleRule::List(FILE* out, int32_t aIndent) const
 }
 #endif
 
-NS_IMETHODIMP
+void
 StyleRule::GetCssText(nsAString& aCssText)
 {
   if (mSelector) {
@@ -1390,33 +1547,29 @@ StyleRule::GetCssText(nsAString& aCssText)
   }
   aCssText.Append(char16_t(' '));
   aCssText.Append(char16_t('}'));
-  return NS_OK;
 }
 
-NS_IMETHODIMP
+void
 StyleRule::SetCssText(const nsAString& aCssText)
 {
   // XXX TBI - need to re-parse rule & declaration
-  return NS_OK;
 }
 
-NS_IMETHODIMP
+void
 StyleRule::GetSelectorText(nsAString& aSelectorText)
 {
   if (mSelector)
     mSelector->ToString(aSelectorText, GetStyleSheet());
   else
     aSelectorText.Truncate();
-  return NS_OK;
 }
 
-NS_IMETHODIMP
+void
 StyleRule::SetSelectorText(const nsAString& aSelectorText)
 {
   // XXX TBI - get a parser and re-parse the selectors,
   // XXX then need to re-compute the cascade
   // XXX and dirty sheet
-  return NS_OK;
 }
 
 /* virtual */ size_t
diff --git a/layout/style/StyleRule.h b/layout/style/StyleRule.h
index 703f6108da67..7445f4d4812a 100644
--- a/layout/style/StyleRule.h
+++ b/layout/style/StyleRule.h
@@ -13,14 +13,12 @@
 
 #include "mozilla/Attributes.h"
 #include "mozilla/MemoryReporting.h"
-#include "mozilla/UniquePtr.h"
 #include "mozilla/css/Rule.h"
 
 #include "nsString.h"
 #include "nsCOMPtr.h"
 #include "nsCSSPseudoElements.h"
 #include "nsIStyleRule.h"
-#include "nsICSSStyleRuleDOMWrapper.h"
 
 class nsIAtom;
 struct nsCSSSelectorList;
@@ -304,15 +302,13 @@ private:
 { 0x464bab7a, 0x2fce, 0x4f30, \
   { 0xab, 0x44, 0xb7, 0xa5, 0xf3, 0xaa, 0xe5, 0x7d } }
 
-class DOMCSSDeclarationImpl;
-
 namespace mozilla {
 namespace css {
 
 class Declaration;
+class DOMCSSStyleRule;
 
 class StyleRule final : public Rule
-                      , public nsICSSStyleRuleDOMWrapper
 {
  public:
   StyleRule(nsCSSSelectorList* aSelector,
@@ -325,15 +321,9 @@ public:
   NS_DECLARE_STATIC_IID_ACCESSOR(NS_CSS_STYLE_RULE_IMPL_CID)
 
   NS_DECL_ISUPPORTS_INHERITED
-  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_INHERITED(StyleRule, Rule)
+  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(StyleRule, Rule)
   virtual bool IsCCLeaf() const override;
 
-  NS_DECL_NSIDOMCSSRULE
-  NS_DECL_NSIDOMCSSSTYLERULE
-
-  // nsICSSStyleRuleDOMWrapper
-  NS_IMETHOD GetCSSStyleRule(StyleRule **aResult) override;
-
   // null for style attribute
   nsCSSSelectorList* Selector() { return mSelector; }
 
@@ -341,6 +331,12 @@ public:
 
   void SetDeclaration(Declaration* aDecl);
 
+  // hooks for DOM rule
+  void GetCssText(nsAString& aCssText);
+  void SetCssText(const nsAString& aCssText);
+  void GetSelectorText(nsAString& aSelectorText);
+  void SetSelectorText(const nsAString& aSelectorText);
+
   virtual int32_t GetType() const override;
 
   CSSStyleSheet* GetStyleSheet() const
@@ -372,9 +368,7 @@ private:
 private:
   nsCSSSelectorList*      mSelector; // null for style attribute
   RefPtr<Declaration>     mDeclaration;
-
-  // We own it, and it aggregates its refcount with us.
-  UniquePtr<DOMCSSDeclarationImpl> mDOMDeclaration;
+  RefPtr<DOMCSSStyleRule> mDOMRule;
 
 private:
   StyleRule& operator=(const StyleRule& aCopy) = delete;