diff --git a/layout/style/RuleCascadeData.cpp b/layout/style/RuleCascadeData.cpp
index 851446bf5e..fb39141acc 100644
--- a/layout/style/RuleCascadeData.cpp
+++ b/layout/style/RuleCascadeData.cpp
@@ -786,7 +786,7 @@ AtomSelector_CIMatchEntry(const PLDHashEntryHdr* hdr, const void* key)
   AtomSelector_InitEntry
 };
 
-RuleCascadeData::RuleCascadeData(nsIAtom* aMedium, bool aQuirksMode)
+RuleCascadeData::RuleCascadeData(bool aQuirksMode)
   : mRuleHash(aQuirksMode)
   , mStateSelectors()
   , mSelectorDocumentStates(0)
@@ -803,7 +803,6 @@ RuleCascadeData::RuleCascadeData(nsIAtom* aMedium, bool aQuirksMode)
   , mXULTreeRules(&RuleHash::TagTable_Ops, sizeof(RuleHashTagTableEntry))
   , mKeyframesRuleTable()
   , mCounterStyleRuleTable()
-  , mCacheKey(aMedium)
   , mQuirksMode(aQuirksMode)
 {
   memset(mPseudoElementRuleHashes, 0, sizeof(mPseudoElementRuleHashes));
@@ -1559,7 +1558,8 @@ CascadeEnumData::CascadeEnumData(nsPresContext* aPresContext,
                                  nsTArray<css::DocumentRule*>& aDocumentRules,
                                  nsDocumentRuleResultCacheKey& aDocumentKey,
                                  SheetType aSheetType,
-                                 bool aMustGatherDocumentRules)
+                                 bool aMustGatherDocumentRules,
+                                 nsMediaQueryResultCacheKey& aCacheKey)
   : mPresContext(aPresContext)
   , mName(aName)
   , mIsAnonymous(mName.IsEmpty())
@@ -1575,6 +1575,7 @@ CascadeEnumData::CascadeEnumData(nsPresContext* aPresContext,
   , mSheetType(aSheetType)
   , mMustGatherDocumentRules(aMustGatherDocumentRules)
   , mRulesByWeight(&sRulesByWeightOps, sizeof(RuleByWeightEntry), 32)
+  , mCacheKey(aCacheKey)
 {
   Initialize();
 }
@@ -1584,7 +1585,8 @@ CascadeEnumData::CascadeEnumData(nsPresContext* aPresContext,
                                  nsTArray<css::DocumentRule*>& aDocumentRules,
                                  nsDocumentRuleResultCacheKey& aDocumentKey,
                                  SheetType aSheetType,
-                                 bool aMustGatherDocumentRules)
+                                 bool aMustGatherDocumentRules,
+                                 nsMediaQueryResultCacheKey& aCacheKey)
   : mPresContext(aPresContext)
   , mContainer(aContainer)
   , mIsAnonymous(false)
@@ -1599,6 +1601,7 @@ CascadeEnumData::CascadeEnumData(nsPresContext* aPresContext,
   , mSheetType(aSheetType)
   , mMustGatherDocumentRules(aMustGatherDocumentRules)
   , mRulesByWeight(&sRulesByWeightOps, sizeof(RuleByWeightEntry), 32)
+  , mCacheKey(aCacheKey)
 {
   Initialize();
 }
@@ -1630,7 +1633,8 @@ CascadeEnumData::CreateNamedChildLayer(const nsTArray<nsString>& aPath)
                                      mDocumentRules,
                                      mDocumentCacheKey,
                                      mSheetType,
-                                     mMustGatherDocumentRules);
+                                     mMustGatherDocumentRules,
+                                     mCacheKey);
     mPreLayers.AppendElement(childLayer);
     mLayers.Put(name, childLayer);
   }
@@ -1660,7 +1664,8 @@ CascadeEnumData::CreateAnonymousChildLayer()
                                                     mDocumentRules,
                                                     mDocumentCacheKey,
                                                     mSheetType,
-                                                    mMustGatherDocumentRules);
+                                                    mMustGatherDocumentRules,
+                                                    mCacheKey);
   mPreLayers.AppendElement(childLayer);
   return childLayer;
 }
@@ -1773,8 +1778,7 @@ CascadeEnumData::Flatten()
 void
 CascadeEnumData::Initialize()
 {
-  mData = new RuleCascadeData(mPresContext->Medium(),
-                              eCompatibility_NavQuirks ==
+  mData = new RuleCascadeData(eCompatibility_NavQuirks ==
                                 mPresContext->CompatibilityMode());
 
   // Initialize our arena
diff --git a/layout/style/RuleCascadeData.h b/layout/style/RuleCascadeData.h
index 3358c4efa5..75e035d970 100644
--- a/layout/style/RuleCascadeData.h
+++ b/layout/style/RuleCascadeData.h
@@ -254,7 +254,7 @@ struct AttributeEnumData
 
 struct RuleCascadeData
 {
-  RuleCascadeData(nsIAtom* aMedium, bool aQuirksMode);
+  RuleCascadeData(bool aQuirksMode);
   ~RuleCascadeData();
 
   size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const;
@@ -286,8 +286,6 @@ struct RuleCascadeData
   // Returns null only on allocation failure.
   nsTArray<SelectorPair>* AttributeListFor(nsIAtom* aAttribute);
 
-  nsMediaQueryResultCacheKey mCacheKey;
-
   const bool mQuirksMode;
 
   void RulesMatching(ElementRuleProcessorData* aData);
@@ -326,8 +324,9 @@ private:
 
 struct ResolvedRuleCascades
 {
-  ResolvedRuleCascades()
+  ResolvedRuleCascades(nsIAtom* aMedium)
     : mUnlayered(nullptr)
+    , mCacheKey(aMedium)
     , mNext(nullptr)
   {
   }
@@ -341,6 +340,7 @@ struct ResolvedRuleCascades
 
   nsTArray<RuleCascadeData*> mOrderedData;
   RuleCascadeData* mUnlayered;
+  nsMediaQueryResultCacheKey mCacheKey;
   ResolvedRuleCascades* mNext; // for a different medium
 
   size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const;
@@ -358,14 +358,16 @@ struct CascadeEnumData
                   nsTArray<css::DocumentRule*>& aDocumentRules,
                   nsDocumentRuleResultCacheKey& aDocumentKey,
                   SheetType aSheetType,
-                  bool aMustGatherDocumentRules);
+                  bool aMustGatherDocumentRules,
+                  nsMediaQueryResultCacheKey& aCacheKey);
 
   CascadeEnumData(nsPresContext* aPresContext,
                   nsAutoPtr<ResolvedRuleCascades>& aContainer,
                   nsTArray<css::DocumentRule*>& aDocumentRules,
                   nsDocumentRuleResultCacheKey& aDocumentKey,
                   SheetType aSheetType,
-                  bool aMustGatherDocumentRules);
+                  bool aMustGatherDocumentRules,
+                  nsMediaQueryResultCacheKey& aCacheKey);
 
   ~CascadeEnumData();
 
@@ -380,6 +382,7 @@ struct CascadeEnumData
   nsTArray<css::StyleRule*> mStyleRules;
   nsTArray<css::DocumentRule*>& mDocumentRules;
   nsDocumentRuleResultCacheKey& mDocumentCacheKey;
+  nsMediaQueryResultCacheKey& mCacheKey;
   SheetType mSheetType;
   bool mMustGatherDocumentRules;
 
diff --git a/layout/style/nsCSSRuleProcessor.cpp b/layout/style/nsCSSRuleProcessor.cpp
index ac5fdf86dd..b5913181a3 100644
--- a/layout/style/nsCSSRuleProcessor.cpp
+++ b/layout/style/nsCSSRuleProcessor.cpp
@@ -335,7 +335,7 @@ nsCSSRuleProcessor::MediumFeaturesChanged(nsPresContext* aPresContext)
     // order hasn't changed).  Other cases will do a restyle anyway, so
     // we shouldn't need to worry about posting a second.
     return !mRuleCascades || // all sheets gone, but we had sheets before
-           mRuleCascades->mUnlayered->mCacheKey != *previousCacheKey;
+           mRuleCascades->mCacheKey != *previousCacheKey;
   }
 
   return false;
@@ -361,11 +361,11 @@ nsCSSRuleProcessor::CloneMQCacheKey()
     return UniquePtr<nsMediaQueryResultCacheKey>();
   }
 
-  if (!c->mUnlayered->mCacheKey.HasFeatureConditions()) {
+  if (!c->mCacheKey.HasFeatureConditions()) {
     return UniquePtr<nsMediaQueryResultCacheKey>();
   }
 
-  return MakeUnique<nsMediaQueryResultCacheKey>(c->mUnlayered->mCacheKey);
+  return MakeUnique<nsMediaQueryResultCacheKey>(c->mCacheKey);
 }
 
 /* virtual */ size_t
@@ -608,7 +608,7 @@ CascadeRuleEnumFunc(css::Rule* aRule, void* aData)
              css::Rule::SUPPORTS_RULE == type) {
     css::GroupRule* groupRule = static_cast<css::GroupRule*>(aRule);
     const bool use = groupRule->UseForPresentation(layer->mPresContext,
-                                                   layer->mData->mCacheKey);
+                                                   layer->mCacheKey);
     if (use || layer->mMustGatherDocumentRules) {
       if (!groupRule->EnumerateRulesForwards(
             use ? CascadeRuleEnumFunc : GatherDocRuleEnumFunc, aData)) {
@@ -633,7 +633,7 @@ CascadeRuleEnumFunc(css::Rule* aRule, void* aData)
                                      ? layer->CreateAnonymousChildLayer()
                                      : layer->CreateNamedChildLayer(path);
     const bool use = layerRule->UseForPresentation(layer->mPresContext,
-                                                   layer->mData->mCacheKey);
+                                                   layer->mCacheKey);
     if (use || layer->mMustGatherDocumentRules) {
       if (!layerRule->EnumerateRulesForwards(
             use ? CascadeRuleEnumFunc : GatherDocRuleEnumFunc, targetLayer)) {
@@ -698,7 +698,7 @@ nsCSSRuleProcessor::CascadeSheet(CSSStyleSheet* aSheet, CascadeEnumData* aLayer)
 {
   if (aSheet->IsApplicable() &&
       aSheet->UseForPresentation(aLayer->mPresContext,
-                                 aLayer->mData->mCacheKey) &&
+                                 aLayer->mCacheKey) &&
       aSheet->mInner) {
     CSSStyleSheet* child = aSheet->mInner->mFirstChild;
     while (child) {
@@ -744,7 +744,7 @@ nsCSSRuleProcessor::RefreshRuleCascade(nsPresContext* aPresContext)
   for (ResolvedRuleCascades** cascadep = &mRuleCascades, *cascade;
         (cascade = *cascadep);
         cascadep = &cascade->mNext) {
-    if (cascade->mUnlayered->mCacheKey.Matches(aPresContext)) {
+    if (cascade->mCacheKey.Matches(aPresContext)) {
       // Ensure that the current one is always mRuleCascades.
       *cascadep = cascade->mNext;
       cascade->mNext = mRuleCascades;
@@ -760,14 +760,15 @@ nsCSSRuleProcessor::RefreshRuleCascade(nsPresContext* aPresContext)
   mPreviousCacheKey = nullptr;
 
   if (mSheets.Length() != 0) {
-    nsAutoPtr<ResolvedRuleCascades> resolvedCascade =
-      new ResolvedRuleCascades();
+    nsAutoPtr<ResolvedRuleCascades> resolvedCascade(
+      new ResolvedRuleCascades(aPresContext->Medium()));
     CascadeEnumData unlayered(aPresContext,
                               resolvedCascade,
                               mDocumentRules,
                               mDocumentCacheKey,
                               mSheetType,
-                              mMustGatherDocumentRules);
+                              mMustGatherDocumentRules,
+                              resolvedCascade->mCacheKey);
     if (unlayered.mData) {
       for (uint32_t i = 0; i < mSheets.Length(); ++i) {
         if (!CascadeSheet(mSheets.ElementAt(i), &unlayered)) {