diff --git a/dom/base/nsWrapperCache.h b/dom/base/nsWrapperCache.h
index 8bdc1b93b6..ef67e91ddb 100644
--- a/dom/base/nsWrapperCache.h
+++ b/dom/base/nsWrapperCache.h
@@ -144,7 +144,7 @@ public:
     }
   }
 
-  bool PreservingWrapper()
+  bool PreservingWrapper() const
   {
     return HasWrapperFlag(WRAPPER_BIT_PRESERVED);
   }
diff --git a/layout/style/CSSStyleSheet.cpp b/layout/style/CSSStyleSheet.cpp
index 5b8a9912fc..bca4820e2e 100644
--- a/layout/style/CSSStyleSheet.cpp
+++ b/layout/style/CSSStyleSheet.cpp
@@ -1238,8 +1238,10 @@ CSSStyleSheet::TraverseInner(nsCycleCollectionTraversalCallback &cb)
 
   const nsCOMArray<css::Rule>& rules = mInner->mOrderedRules;
   for (int32_t i = 0, count = rules.Count(); i < count; ++i) {
-    NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(cb, "mOrderedRules[i]");
-    cb.NoteXPCOMChild(rules[i]->GetExistingDOMRule());
+    if (!rules[i]->IsCCLeaf()) {
+      NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(cb, "mOrderedRules[i]");
+      cb.NoteXPCOMChild(rules[i]);
+    }
   }
 }
 
diff --git a/layout/style/Declaration.h b/layout/style/Declaration.h
index e7701e7380..f5b43439fd 100644
--- a/layout/style/Declaration.h
+++ b/layout/style/Declaration.h
@@ -96,6 +96,8 @@ public:
 
   NS_DECLARE_STATIC_IID_ACCESSOR(NS_CSS_DECLARATION_IMPL_CID)
 
+  // If this ever becomes cycle-collected, please change the CC implementation
+  // for StyleRule to traverse it.
   NS_DECL_ISUPPORTS
 
 private:
diff --git a/layout/style/GroupRule.h b/layout/style/GroupRule.h
index ec781fae68..d9770dd1ec 100644
--- a/layout/style/GroupRule.h
+++ b/layout/style/GroupRule.h
@@ -38,8 +38,9 @@ protected:
   virtual ~GroupRule();
 public:
 
-  NS_DECL_CYCLE_COLLECTION_CLASS(GroupRule)
-  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(GroupRule, Rule)
+  NS_DECL_ISUPPORTS_INHERITED
+  virtual bool IsCCLeaf() const override;
 
   // implement part of Rule
   DECL_STYLE_RULE_INHERIT_NO_DOMRULE
diff --git a/layout/style/ImportRule.h b/layout/style/ImportRule.h
index f0803ba9d0..4db2bdf44d 100644
--- a/layout/style/ImportRule.h
+++ b/layout/style/ImportRule.h
@@ -34,8 +34,9 @@ private:
   ImportRule(const ImportRule& aCopy);
   ~ImportRule();
 public:
-  NS_DECL_CYCLE_COLLECTION_CLASS_AMBIGUOUS(ImportRule, mozilla::css::Rule)
-  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(ImportRule, Rule)
+  NS_DECL_ISUPPORTS_INHERITED
+  virtual bool IsCCLeaf() const override;
 
   DECL_STYLE_RULE_INHERIT
 
diff --git a/layout/style/NameSpaceRule.h b/layout/style/NameSpaceRule.h
index 92d910cf5d..2165796071 100644
--- a/layout/style/NameSpaceRule.h
+++ b/layout/style/NameSpaceRule.h
@@ -37,7 +37,8 @@ private:
 public:
   NS_DECLARE_STATIC_IID_ACCESSOR(NS_CSS_NAMESPACE_RULE_IMPL_CID)
 
-  NS_DECL_ISUPPORTS
+  NS_DECL_ISUPPORTS_INHERITED
+  virtual bool IsCCLeaf() const override;
 
   // Rule methods
   DECL_STYLE_RULE_INHERIT
diff --git a/layout/style/Rule.h b/layout/style/Rule.h
index 7abe71174e..ac72297765 100644
--- a/layout/style/Rule.h
+++ b/layout/style/Rule.h
@@ -52,6 +52,12 @@ protected:
 
 public:
 
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_SKIPPABLE_CLASS(Rule)
+  // Return true if this rule is known to be a cycle collection leaf, in the
+  // sense that it doesn't have any outgoing owning edges.
+  virtual bool IsCCLeaf() const MOZ_MUST_OVERRIDE;
+
 #ifdef DEBUG
   virtual void List(FILE* out = stdout, int32_t aIndent = 0) const = 0;
 #endif
@@ -124,6 +130,9 @@ public:
     const MOZ_MUST_OVERRIDE = 0;
 
 protected:
+  // True if we're known-live for cycle collection purposes.
+  bool IsKnownLive() const;
+
   // This is sometimes null (e.g., for style attributes).
   CSSStyleSheet*    mSheet;
   // When the parent GroupRule is destroyed, it will call SetParentRule(nullptr)
diff --git a/layout/style/StyleRule.cpp b/layout/style/StyleRule.cpp
index 5c3ec354d5..df25a0c5c6 100644
--- a/layout/style/StyleRule.cpp
+++ b/layout/style/StyleRule.cpp
@@ -1460,8 +1460,15 @@ StyleRule::StyleRule(const StyleRule& aCopy)
 StyleRule::~StyleRule()
 {
   delete mSelector;
+  DropReferences();
+}
+
+void
+StyleRule::DropReferences()
+{
   if (mDOMRule) {
     mDOMRule->DOMDeclaration()->DropReference();
+    mDOMRule = nullptr;
   }
 
   if (mDeclaration) {
@@ -1470,18 +1477,36 @@ StyleRule::~StyleRule()
 }
 
 // QueryInterface implementation for StyleRule
-NS_INTERFACE_MAP_BEGIN(StyleRule)
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION_INHERITED(StyleRule)
   if (aIID.Equals(NS_GET_IID(mozilla::css::StyleRule))) {
     *aInstancePtr = this;
     NS_ADDREF_THIS();
     return NS_OK;
   }
   else
-  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, mozilla::css::Rule)
-NS_INTERFACE_MAP_END
+NS_INTERFACE_MAP_END_INHERITING(Rule)
 
-NS_IMPL_ADDREF(StyleRule)
-NS_IMPL_RELEASE(StyleRule)
+NS_IMPL_ADDREF_INHERITED(StyleRule, Rule)
+NS_IMPL_RELEASE_INHERITED(StyleRule, Rule)
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(StyleRule)
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(StyleRule, Rule)
+  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
+StyleRule::IsCCLeaf() const
+{
+  if (!Rule::IsCCLeaf()) {
+    return false;
+  }
+
+  return !mDOMRule || !mDOMRule->DOMDeclaration()->PreservingWrapper();
+}
 
 /* virtual */ int32_t
 StyleRule::GetType() const
diff --git a/layout/style/StyleRule.h b/layout/style/StyleRule.h
index f2af2717b5..ef21acc137 100644
--- a/layout/style/StyleRule.h
+++ b/layout/style/StyleRule.h
@@ -334,7 +334,9 @@ private:
 public:
   NS_DECLARE_STATIC_IID_ACCESSOR(NS_CSS_STYLE_RULE_IMPL_CID)
 
-  NS_DECL_ISUPPORTS
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(StyleRule, Rule)
+  virtual bool IsCCLeaf() const override;
 
   // null for style attribute
   nsCSSSelectorList* Selector() { return mSelector; }
@@ -366,6 +368,10 @@ public:
 private:
   ~StyleRule();
 
+  // Drop our references to mDeclaration and mRule, and let them know we're
+  // doing that.
+  void DropReferences();
+
 private:
   nsCSSSelectorList*      mSelector; // null for style attribute
   RefPtr<Declaration>     mDeclaration;
diff --git a/layout/style/nsCSSRules.cpp b/layout/style/nsCSSRules.cpp
index 1642516979..f2fd229167 100644
--- a/layout/style/nsCSSRules.cpp
+++ b/layout/style/nsCSSRules.cpp
@@ -37,6 +37,7 @@
 #include "nsFont.h"
 #include "nsIURI.h"
 #include "mozAutoDocUpdate.h"
+#include "nsCCUncollectableMarker.h"
 
 using namespace mozilla;
 using namespace mozilla::dom;
@@ -55,6 +56,52 @@ IMPL_STYLE_RULE_INHERIT_GET_DOM_RULE_WEAK(class_, super_)
 namespace mozilla {
 namespace css {
 
+NS_IMPL_CYCLE_COLLECTING_ADDREF(Rule)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(Rule)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(Rule)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+NS_IMPL_CYCLE_COLLECTION_0(Rule)
+
+bool
+Rule::IsCCLeaf() const
+{
+  return true;
+}
+
+bool
+Rule::IsKnownLive() const
+{
+  StyleSheet* sheet = GetStyleSheet();
+  if (!sheet) {
+    return false;
+  }
+
+  if (!sheet->IsOwnedByDocument()) {
+    return false;
+  }
+
+  return nsCCUncollectableMarker::InGeneration(
+    sheet->GetAssociatedDocument()->GetMarkedCCGeneration());
+}
+
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_BEGIN(Rule)
+  return tmp->IsCCLeaf() || tmp->IsKnownLive();
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_END
+
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_IN_CC_BEGIN(Rule)
+  // Note that we can't make use of IsKnownLive() here directly, because we may
+  // be subclassed by something that needs tracing.  Once we have a wrapper
+  // cache we should be able to do better here.
+  return tmp->IsCCLeaf();
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_IN_CC_END
+
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_THIS_BEGIN(Rule)
+  return tmp->IsCCLeaf() || tmp->IsKnownLive();
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_THIS_END
+
 /* virtual */ void
 Rule::SetStyleSheet(CSSStyleSheet* aSheet)
 {
@@ -199,16 +246,22 @@ ImportRule::~ImportRule()
   }
 }
 
-NS_IMPL_CYCLE_COLLECTING_ADDREF(ImportRule)
-NS_IMPL_CYCLE_COLLECTING_RELEASE(ImportRule)
+NS_IMPL_ADDREF_INHERITED(ImportRule, Rule)
+NS_IMPL_RELEASE_INHERITED(ImportRule, Rule)
+
+bool
+ImportRule::IsCCLeaf() const
+{
+  // We're not a leaf.
+  return false;
+}
 
 // QueryInterface implementation for ImportRule
-NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(ImportRule)
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION_INHERITED(ImportRule)
   NS_INTERFACE_MAP_ENTRY(nsIDOMCSSRule)
   NS_INTERFACE_MAP_ENTRY(nsIDOMCSSImportRule)
-  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, mozilla::css::Rule)
   NS_DOM_INTERFACE_MAP_ENTRY_CLASSINFO(CSSImportRule)
-NS_INTERFACE_MAP_END
+NS_INTERFACE_MAP_END_INHERITING(Rule)
 
 IMPL_STYLE_RULE_INHERIT(ImportRule, Rule)
 
@@ -393,11 +446,18 @@ GroupRule::~GroupRule()
   }
 }
 
-NS_IMPL_CYCLE_COLLECTING_ADDREF(GroupRule)
-NS_IMPL_CYCLE_COLLECTING_RELEASE(GroupRule)
+NS_IMPL_ADDREF_INHERITED(GroupRule, Rule)
+NS_IMPL_RELEASE_INHERITED(GroupRule, Rule)
 
-NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(GroupRule)
-NS_INTERFACE_MAP_END
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION_INHERITED(GroupRule)
+NS_INTERFACE_MAP_END_INHERITING(Rule)
+
+bool
+GroupRule::IsCCLeaf() const
+{
+  // Let's not worry for now about sorting out whether we're a leaf or not.
+  return false;
+}
 
 static bool
 SetStyleSheetReference(Rule* aRule, void* aSheet)
@@ -409,7 +469,7 @@ SetStyleSheetReference(Rule* aRule, void* aSheet)
 
 NS_IMPL_CYCLE_COLLECTION_CLASS(GroupRule)
 
-NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(GroupRule)
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(GroupRule, Rule)
   tmp->mRules.EnumerateForwards(SetParentRuleReference, nullptr);
   // If tmp does not have a stylesheet, neither do its descendants.  In that
   // case, don't try to null out their stylesheet, to avoid O(N^2) behavior in
@@ -427,11 +487,13 @@ NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(GroupRule)
   }
 NS_IMPL_CYCLE_COLLECTION_UNLINK_END
 
-NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(GroupRule)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(GroupRule, Rule)
   const nsCOMArray<Rule>& rules = tmp->mRules;
   for (int32_t i = 0, count = rules.Count(); i < count; ++i) {
-    NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(cb, "mRules[i]");
-    cb.NoteXPCOMChild(rules[i]->GetExistingDOMRule());
+    if (!rules[i]->IsCCLeaf()) {
+      NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(cb, "mRules[i]");
+      cb.NoteXPCOMChild(rules[i]);
+    }
   }
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mRuleCollection)
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
@@ -624,22 +686,11 @@ NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION_INHERITED(MediaRule)
   NS_INTERFACE_MAP_ENTRY(nsIDOMCSSGroupingRule)
   NS_INTERFACE_MAP_ENTRY(nsIDOMCSSConditionRule)
   NS_INTERFACE_MAP_ENTRY(nsIDOMCSSMediaRule)
-  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, mozilla::css::Rule)
   NS_DOM_INTERFACE_MAP_ENTRY_CLASSINFO(CSSMediaRule)
 NS_INTERFACE_MAP_END_INHERITING(GroupRule)
 
-NS_IMPL_CYCLE_COLLECTION_CLASS(MediaRule)
-
-NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(MediaRule, GroupRule)
-  if (tmp->mMedia) {
-    tmp->mMedia->SetStyleSheet(nullptr);
-    tmp->mMedia = nullptr;
-  }
-NS_IMPL_CYCLE_COLLECTION_UNLINK_END
-
-NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(MediaRule, GroupRule)
-  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mMedia)
-NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+NS_IMPL_CYCLE_COLLECTION_INHERITED(MediaRule, GroupRule,
+                                   mMedia)
 
 /* virtual */ void
 MediaRule::SetStyleSheet(CSSStyleSheet* aSheet)
@@ -1110,10 +1161,12 @@ NameSpaceRule::~NameSpaceRule()
 {
 }
 
-NS_IMPL_ADDREF(NameSpaceRule)
-NS_IMPL_RELEASE(NameSpaceRule)
+NS_IMPL_ADDREF_INHERITED(NameSpaceRule, Rule)
+NS_IMPL_RELEASE_INHERITED(NameSpaceRule, Rule)
 
 // QueryInterface implementation for NameSpaceRule
+// If this ever gets its own cycle-collection bits, reevaluate our IsCCLeaf
+// implementation.
 NS_INTERFACE_MAP_BEGIN(NameSpaceRule)
   if (aIID.Equals(NS_GET_IID(css::NameSpaceRule))) {
     *aInstancePtr = this;
@@ -1122,9 +1175,14 @@ NS_INTERFACE_MAP_BEGIN(NameSpaceRule)
   }
   else
   NS_INTERFACE_MAP_ENTRY(nsIDOMCSSRule)
-  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, mozilla::css::Rule)
   NS_DOM_INTERFACE_MAP_ENTRY_CLASSINFO(CSSNameSpaceRule)
-NS_INTERFACE_MAP_END
+NS_INTERFACE_MAP_END_INHERITING(Rule)
+
+bool
+NameSpaceRule::IsCCLeaf() const
+{
+  return Rule::IsCCLeaf();
+}
 
 IMPL_STYLE_RULE_INHERIT(NameSpaceRule, Rule)
 
@@ -1539,35 +1597,52 @@ nsCSSFontFaceRule::Clone() const
   return clone.forget();
 }
 
-NS_IMPL_CYCLE_COLLECTING_ADDREF(nsCSSFontFaceRule)
-NS_IMPL_CYCLE_COLLECTING_RELEASE(nsCSSFontFaceRule)
+NS_IMPL_ADDREF_INHERITED(nsCSSFontFaceRule, mozilla::css::Rule)
+NS_IMPL_RELEASE_INHERITED(nsCSSFontFaceRule, mozilla::css::Rule)
 
 NS_IMPL_CYCLE_COLLECTION_CLASS(nsCSSFontFaceRule)
 
-NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(nsCSSFontFaceRule)
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN_INHERITED(nsCSSFontFaceRule,
+                                               mozilla::css::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.
   tmp->mDecl.TraceWrapper(aCallbacks, aClosure);
 NS_IMPL_CYCLE_COLLECTION_TRACE_END
 
-NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(nsCSSFontFaceRule)
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(nsCSSFontFaceRule,
+                                                mozilla::css::Rule)
+  // Keep this in sync with IsCCLeaf.
+
   // 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->mDecl.ReleaseWrapper(static_cast<nsISupports*>(p));
 NS_IMPL_CYCLE_COLLECTION_UNLINK_END
 
-NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(nsCSSFontFaceRule)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(nsCSSFontFaceRule,
+                                                  mozilla::css::Rule)
+  // Keep this in sync with IsCCLeaf.
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 
+bool
+nsCSSFontFaceRule::IsCCLeaf() const
+{
+  if (!Rule::IsCCLeaf()) {
+    return false;
+  }
+
+  return !mDecl.PreservingWrapper();
+}
+
 // QueryInterface implementation for nsCSSFontFaceRule
-NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(nsCSSFontFaceRule)
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION_INHERITED(nsCSSFontFaceRule)
   NS_INTERFACE_MAP_ENTRY(nsIDOMCSSFontFaceRule)
   NS_INTERFACE_MAP_ENTRY(nsIDOMCSSRule)
-  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, mozilla::css::Rule)
   NS_DOM_INTERFACE_MAP_ENTRY_CLASSINFO(CSSFontFaceRule)
-NS_INTERFACE_MAP_END
+NS_INTERFACE_MAP_END_INHERITING(Rule)
 
 IMPL_STYLE_RULE_INHERIT(nsCSSFontFaceRule, Rule)
 
@@ -1702,16 +1777,23 @@ nsCSSFontFeatureValuesRule::Clone() const
   return clone.forget();
 }
 
-NS_IMPL_ADDREF(nsCSSFontFeatureValuesRule)
-NS_IMPL_RELEASE(nsCSSFontFeatureValuesRule)
+NS_IMPL_ADDREF_INHERITED(nsCSSFontFeatureValuesRule, mozilla::css::Rule)
+NS_IMPL_RELEASE_INHERITED(nsCSSFontFeatureValuesRule, mozilla::css::Rule)
 
 // QueryInterface implementation for nsCSSFontFeatureValuesRule
+// If this ever gets its own cycle-collection bits, reevaluate our IsCCLeaf
+// implementation.
 NS_INTERFACE_MAP_BEGIN(nsCSSFontFeatureValuesRule)
   NS_INTERFACE_MAP_ENTRY(nsIDOMCSSFontFeatureValuesRule)
   NS_INTERFACE_MAP_ENTRY(nsIDOMCSSRule)
-  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, mozilla::css::Rule)
   NS_DOM_INTERFACE_MAP_ENTRY_CLASSINFO(CSSFontFeatureValuesRule)
-NS_INTERFACE_MAP_END
+NS_INTERFACE_MAP_END_INHERITING(mozilla::css::Rule)
+
+bool
+nsCSSFontFeatureValuesRule::IsCCLeaf() const
+{
+  return Rule::IsCCLeaf();
+}
 
 IMPL_STYLE_RULE_INHERIT(nsCSSFontFeatureValuesRule, Rule)
 
@@ -2037,28 +2119,35 @@ nsCSSKeyframeRule::Clone() const
   return clone.forget();
 }
 
-NS_IMPL_CYCLE_COLLECTING_ADDREF(nsCSSKeyframeRule)
-NS_IMPL_CYCLE_COLLECTING_RELEASE(nsCSSKeyframeRule)
+NS_IMPL_ADDREF_INHERITED(nsCSSKeyframeRule, mozilla::css::Rule)
+NS_IMPL_RELEASE_INHERITED(nsCSSKeyframeRule, mozilla::css::Rule)
 
 NS_IMPL_CYCLE_COLLECTION_CLASS(nsCSSKeyframeRule)
 
-NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(nsCSSKeyframeRule)
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(nsCSSKeyframeRule, mozilla::css::Rule)
   if (tmp->mDOMDeclaration) {
     tmp->mDOMDeclaration->DropReference();
     tmp->mDOMDeclaration = nullptr;
   }
 NS_IMPL_CYCLE_COLLECTION_UNLINK_END
-NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(nsCSSKeyframeRule)
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(nsCSSKeyframeRule, mozilla::css::Rule)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mDOMDeclaration)
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 
+bool
+nsCSSKeyframeRule::IsCCLeaf() const
+{
+  // Let's not worry about figuring out whether we're a leaf or not.
+  return false;
+}
+
 // QueryInterface implementation for nsCSSKeyframeRule
-NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(nsCSSKeyframeRule)
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION_INHERITED(nsCSSKeyframeRule)
   NS_INTERFACE_MAP_ENTRY(nsIDOMCSSKeyframeRule)
   NS_INTERFACE_MAP_ENTRY(nsIDOMCSSRule)
-  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, mozilla::css::Rule)
   NS_DOM_INTERFACE_MAP_ENTRY_CLASSINFO(CSSKeyframeRule)
-NS_INTERFACE_MAP_END
+NS_INTERFACE_MAP_END_INHERITING(mozilla::css::Rule)
 
 IMPL_STYLE_RULE_INHERIT_GET_DOM_RULE_WEAK(nsCSSKeyframeRule, Rule)
 
@@ -2263,7 +2352,6 @@ NS_IMPL_RELEASE_INHERITED(nsCSSKeyframesRule, css::GroupRule)
 NS_INTERFACE_MAP_BEGIN(nsCSSKeyframesRule)
   NS_INTERFACE_MAP_ENTRY(nsIDOMCSSRule)
   NS_INTERFACE_MAP_ENTRY(nsIDOMCSSKeyframesRule)
-  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, mozilla::css::Rule)
   NS_DOM_INTERFACE_MAP_ENTRY_CLASSINFO(CSSKeyframesRule)
 NS_INTERFACE_MAP_END_INHERITING(GroupRule)
 
@@ -2594,28 +2682,35 @@ nsCSSPageRule::Clone() const
   return clone.forget();
 }
 
-NS_IMPL_CYCLE_COLLECTING_ADDREF(nsCSSPageRule)
-NS_IMPL_CYCLE_COLLECTING_RELEASE(nsCSSPageRule)
+NS_IMPL_ADDREF_INHERITED(nsCSSPageRule, mozilla::css::Rule)
+NS_IMPL_RELEASE_INHERITED(nsCSSPageRule, mozilla::css::Rule)
 
 NS_IMPL_CYCLE_COLLECTION_CLASS(nsCSSPageRule)
 
-NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(nsCSSPageRule)
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(nsCSSPageRule, mozilla::css::Rule)
   if (tmp->mDOMDeclaration) {
     tmp->mDOMDeclaration->DropReference();
     tmp->mDOMDeclaration = nullptr;
   }
 NS_IMPL_CYCLE_COLLECTION_UNLINK_END
-NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(nsCSSPageRule)
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(nsCSSPageRule, mozilla::css::Rule)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mDOMDeclaration)
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 
+bool
+nsCSSPageRule::IsCCLeaf() const
+{
+  // Let's not worry about figuring out whether we're a leaf or not.
+  return false;
+}
+
 // QueryInterface implementation for nsCSSPageRule
-NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(nsCSSPageRule)
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION_INHERITED(nsCSSPageRule)
   NS_INTERFACE_MAP_ENTRY(nsIDOMCSSPageRule)
   NS_INTERFACE_MAP_ENTRY(nsIDOMCSSRule)
-  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, mozilla::css::Rule)
   NS_DOM_INTERFACE_MAP_ENTRY_CLASSINFO(CSSPageRule)
-NS_INTERFACE_MAP_END
+NS_INTERFACE_MAP_END_INHERITING(mozilla::css::Rule)
 
 IMPL_STYLE_RULE_INHERIT_GET_DOM_RULE_WEAK(nsCSSPageRule, Rule)
 
@@ -2786,7 +2881,6 @@ NS_INTERFACE_MAP_BEGIN(CSSSupportsRule)
   NS_INTERFACE_MAP_ENTRY(nsIDOMCSSGroupingRule)
   NS_INTERFACE_MAP_ENTRY(nsIDOMCSSConditionRule)
   NS_INTERFACE_MAP_ENTRY(nsIDOMCSSSupportsRule)
-  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, mozilla::css::Rule)
   NS_DOM_INTERFACE_MAP_ENTRY_CLASSINFO(CSSSupportsRule)
 NS_INTERFACE_MAP_END_INHERITING(GroupRule)
 
@@ -2907,16 +3001,23 @@ nsCSSCounterStyleRule::kGetters[] = {
 #undef CSS_COUNTER_DESC
 };
 
-NS_IMPL_ADDREF(nsCSSCounterStyleRule)
-NS_IMPL_RELEASE(nsCSSCounterStyleRule)
+NS_IMPL_ADDREF_INHERITED(nsCSSCounterStyleRule, mozilla::css::Rule)
+NS_IMPL_RELEASE_INHERITED(nsCSSCounterStyleRule, mozilla::css::Rule)
 
 // QueryInterface implementation for nsCSSCounterStyleRule
+// If this ever gets its own cycle-collection bits, reevaluate our IsCCLeaf
+// implementation.
 NS_INTERFACE_MAP_BEGIN(nsCSSCounterStyleRule)
   NS_INTERFACE_MAP_ENTRY(nsIDOMCSSRule)
   NS_INTERFACE_MAP_ENTRY(nsIDOMCSSCounterStyleRule)
-  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, mozilla::css::Rule)
   NS_DOM_INTERFACE_MAP_ENTRY_CLASSINFO(CSSCounterStyleRule)
-NS_INTERFACE_MAP_END
+NS_INTERFACE_MAP_END_INHERITING(mozilla::css::Rule)
+
+bool
+nsCSSCounterStyleRule::IsCCLeaf() const
+{
+  return Rule::IsCCLeaf();
+}
 
 IMPL_STYLE_RULE_INHERIT(nsCSSCounterStyleRule, css::Rule)
 
diff --git a/layout/style/nsCSSRules.h b/layout/style/nsCSSRules.h
index 9c3196575c..0482603b26 100644
--- a/layout/style/nsCSSRules.h
+++ b/layout/style/nsCSSRules.h
@@ -248,9 +248,9 @@ public:
     // copy everything except our reference count
     : mozilla::css::Rule(aCopy), mDecl(aCopy.mDecl) {}
 
-  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
-  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_AMBIGUOUS(nsCSSFontFaceRule,
-                                                         mozilla::css::Rule)
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_INHERITED(nsCSSFontFaceRule, mozilla::css::Rule)
+  virtual bool IsCCLeaf() const override;
 
   // Rule methods
   DECL_STYLE_RULE_INHERIT
@@ -315,7 +315,8 @@ public:
       mFamilyList(aCopy.mFamilyList),
       mFeatureValues(aCopy.mFeatureValues) {}
 
-  NS_DECL_ISUPPORTS
+  NS_DECL_ISUPPORTS_INHERITED
+  virtual bool IsCCLeaf() const override;
 
   // Rule methods
   DECL_STYLE_RULE_INHERIT
@@ -398,8 +399,9 @@ private:
   nsCSSKeyframeRule(const nsCSSKeyframeRule& aCopy);
   ~nsCSSKeyframeRule();
 public:
-  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
-  NS_DECL_CYCLE_COLLECTION_CLASS_AMBIGUOUS(nsCSSKeyframeRule, mozilla::css::Rule)
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(nsCSSKeyframeRule, mozilla::css::Rule)
+  virtual bool IsCCLeaf() const override;
 
   // Rule methods
   DECL_STYLE_RULE_INHERIT
@@ -526,8 +528,9 @@ private:
   nsCSSPageRule(const nsCSSPageRule& aCopy);
   ~nsCSSPageRule();
 public:
-  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
-  NS_DECL_CYCLE_COLLECTION_CLASS_AMBIGUOUS(nsCSSPageRule, nsIDOMCSSPageRule)
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(nsCSSPageRule, mozilla::css::Rule)
+  virtual bool IsCCLeaf() const override;
 
   // Rule methods
   DECL_STYLE_RULE_INHERIT
@@ -623,7 +626,8 @@ private:
   ~nsCSSCounterStyleRule();
 
 public:
-  NS_DECL_ISUPPORTS
+  NS_DECL_ISUPPORTS_INHERITED
+  virtual bool IsCCLeaf() const override;
 
   // Rule methods
   DECL_STYLE_RULE_INHERIT