--- a/layout/style/CSSStyleSheet.cpp
+++ b/layout/style/CSSStyleSheet.cpp
@@ -1319,43 +1319,16 @@ CSSStyleSheet::AddStyleSet(nsStyleSet* a
 void
 CSSStyleSheet::DropStyleSet(nsStyleSet* aStyleSet)
 {
   DebugOnly<bool> found = mStyleSets.RemoveElement(aStyleSet);
   NS_ASSERTION(found, "didn't find style set");
 }
 
 void
-CSSStyleSheet::SetURIs(nsIURI* aSheetURI, nsIURI* aOriginalSheetURI,
-                       nsIURI* aBaseURI)
-{
-  NS_ASSERTION(mInner->mOrderedRules.Count() == 0 && !mInner->mComplete,
-               "Can't call SetURIs on sheets that are complete or have rules");
-  mInner->SetURIs(aSheetURI, aOriginalSheetURI, aBaseURI);
-}
-
-void
-CSSStyleSheet::SetPrincipal(nsIPrincipal* aPrincipal)
-{
-  mInner->SetPrincipal(aPrincipal);
-}
-
-nsIURI*
-CSSStyleSheet::GetSheetURI() const
-{
-  return mInner->mSheetURI;
-}
-
-nsIURI*
-CSSStyleSheet::GetBaseURI() const
-{
-  return mInner->mBaseURI;
-}
-
-void
 CSSStyleSheet::GetType(nsString& aType) const
 {
   aType.AssignLiteral("text/css");
 }
 
 bool
 CSSStyleSheet::UseForPresentation(nsPresContext* aPresContext,
                                   nsMediaQueryResultCacheKey& aKey) const
@@ -1374,22 +1347,16 @@ CSSStyleSheet::SetMedia(nsMediaList* aMe
 }
 
 bool
 CSSStyleSheet::HasRules() const
 {
   return StyleRuleCount() != 0;
 }
 
-bool
-CSSStyleSheet::IsApplicable() const
-{
-  return !mDisabled && mInner->mComplete;
-}
-
 void
 CSSStyleSheet::SetEnabled(bool aEnabled)
 {
   // Internal method, so callers must handle BeginUpdate/EndUpdate
   bool oldDisabled = mDisabled;
   mDisabled = !aEnabled;
 
   if (mInner->mComplete && oldDisabled != mDisabled) {
@@ -1402,22 +1369,16 @@ CSSStyleSheet::SetEnabled(bool aEnabled)
 }
 
 CSSStyleSheet*
 CSSStyleSheet::GetParentSheet() const
 {
   return mParent;
 }
 
-nsIDocument*
-CSSStyleSheet::GetOwningDocument() const
-{
-  return mDocument;
-}
-
 void
 CSSStyleSheet::SetOwningDocument(nsIDocument* aDocument)
 { // not ref counted
   mDocument = aDocument;
   // Now set the same document on all our child sheets....
   // XXXbz this is a little bogus; see the XXX comment where we
   // declare mFirstChild.
   for (CSSStyleSheet* child = mInner->mFirstChild;

--- a/layout/style/CSSStyleSheet.h
+++ b/layout/style/CSSStyleSheet.h
@@ -120,44 +120,33 @@ public:
                 const dom::SRIMetadata& aIntegrity);
 
   NS_DECL_CYCLE_COLLECTING_ISUPPORTS
   NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_AMBIGUOUS(CSSStyleSheet,
                                                          nsIDOMCSSStyleSheet)
 
   NS_DECLARE_STATIC_IID_ACCESSOR(NS_CSS_STYLE_SHEET_IMPL_CID)
 
-  nsIURI* GetSheetURI() const;
-  nsIURI* GetBaseURI() const;
   void GetTitle(nsString& aTitle) const;
   void GetType(nsString& aType) const;
   bool HasRules() const;
 
   /**
-   * Whether the sheet is applicable.  A sheet that is not applicable
-   * should never be inserted into a style set.  A sheet may not be
-   * applicable for a variety of reasons including being disabled and
-   * being incomplete.
-   */
-  bool IsApplicable() const;
-
-  /**
    * Set the stylesheet to be enabled.  This may or may not make it
    * applicable.  Note that this WILL inform the sheet's document of
    * its new applicable state if the state changes but WILL NOT call
    * BeginUpdate() or EndUpdate() on the document -- calling those is
    * the caller's responsibility.  This allows use of SetEnabled when
    * batched updates are desired.  If you want updates handled for
    * you, see nsIDOMStyleSheet::SetDisabled().
    */
   void SetEnabled(bool aEnabled);
 
   // style sheet owner info
   CSSStyleSheet* GetParentSheet() const;  // may be null
-  nsIDocument* GetOwningDocument() const;  // may be null
   void SetOwningDocument(nsIDocument* aDocument);
 
   // Find the ID of the owner inner window.
   uint64_t FindOwningWindowInnerID() const;
 #ifdef DEBUG
   void List(FILE* out = stdout, int32_t aIndent = 0) const;
 #endif
 
@@ -167,33 +156,16 @@ public:
   void AppendStyleRule(css::Rule* aRule);
 
   int32_t StyleRuleCount() const;
   css::Rule* GetStyleRuleAt(int32_t aIndex) const;
 
   nsresult DeleteRuleFromGroup(css::GroupRule* aGroup, uint32_t aIndex);
   nsresult InsertRuleIntoGroup(const nsAString& aRule, css::GroupRule* aGroup, uint32_t aIndex, uint32_t* _retval);
 
-  /**
-   * SetURIs must be called on all sheets before parsing into them.
-   * SetURIs may only be called while the sheet is 1) incomplete and 2)
-   * has no rules in it
-   */
-  void SetURIs(nsIURI* aSheetURI, nsIURI* aOriginalSheetURI, nsIURI* aBaseURI);
-
-  /**
-   * SetPrincipal should be called on all sheets before parsing into them.
-   * This can only be called once with a non-null principal.  Calling this with
-   * a null pointer is allowed and is treated as a no-op.
-   */
-  void SetPrincipal(nsIPrincipal* aPrincipal);
-
-  // Principal() never returns a null pointer.
-  nsIPrincipal* Principal() const { return mInner->mPrincipal; }
-
   void SetTitle(const nsAString& aTitle) { mTitle = aTitle; }
   void SetMedia(nsMediaList* aMedia);
 
   void SetOwnerRule(css::ImportRule* aOwnerRule) { mOwnerRule = aOwnerRule; /* Not ref counted */ }
   css::ImportRule* GetOwnerRule() const { return mOwnerRule; }
 
   nsXMLNameSpaceMap* GetNameSpaceMap() const { return mInner->mNameSpaceMap; }
 
@@ -217,23 +189,16 @@ public:
   void DropStyleSet(nsStyleSet* aStyleSet);
 
   /**
    * Like the DOM insertRule() method, but doesn't do any security checks
    */
   nsresult InsertRuleInternal(const nsAString& aRule,
                               uint32_t aIndex, uint32_t* aReturn);
 
-  /* Get the URI this sheet was originally loaded from, if any.  Can
-     return null */
-  nsIURI* GetOriginalURI() const { return mInner->mOriginalSheetURI; }
-
-  // Whether the sheet is for an inline <style> element.
-  bool IsInline() const { return mInner->IsInline(); }
-
   // nsICSSLoaderObserver interface
   NS_IMETHOD StyleSheetLoaded(StyleSheetHandle aSheet, bool aWasAlternate,
                               nsresult aStatus) override;
 
   void EnsureUniqueInner();
 
   // Append all of this sheet's child sheets to aArray.
   void AppendAllChildSheets(nsTArray<CSSStyleSheet*>& aArray);
@@ -252,39 +217,30 @@ public:
   NS_DECL_NSIDOMCSSSTYLESHEET
 
   // Function used as a callback to rebuild our inner's child sheet
   // list after we clone a unique inner for ourselves.
   static bool RebuildChildList(css::Rule* aRule, void* aBuilder);
 
   size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const;
 
-  // Get this style sheet's CORS mode
-  CORSMode GetCORSMode() const { return mInner->mCORSMode; }
-
-  // Get this style sheet's Referrer Policy
-  ReferrerPolicy GetReferrerPolicy() const { return mInner->mReferrerPolicy; }
-
-  // Get this style sheet's integrity metadata
-  void GetIntegrity(dom::SRIMetadata& aResult) const { aResult = mInner->mIntegrity; }
-
   dom::Element* GetScopeElement() const { return mScopeElement; }
   void SetScopeElement(dom::Element* aScopeElement)
   {
     mScopeElement = aScopeElement;
   }
 
   // WebIDL StyleSheet API
   // Our CSSStyleSheet::GetType is a const method, so it ends up
   // ambiguous with with the XPCOM version.  Just disambiguate.
   void GetType(nsString& aType) {
     const_cast<const CSSStyleSheet*>(this)->GetType(aType);
   }
   // Our XPCOM GetHref is fine for WebIDL
-  nsINode* GetOwnerNode() const { return mOwningNode; }
+  using StyleSheet::GetOwnerNode;
   CSSStyleSheet* GetParentStyleSheet() const { return mParent; }
   // Our CSSStyleSheet::GetTitle is a const method, so it ends up
   // ambiguous with with the XPCOM version.  Just disambiguate.
   void GetTitle(nsString& aTitle) {
     const_cast<const CSSStyleSheet*>(this)->GetTitle(aTitle);
   }
   nsMediaList* Media();
   bool Disabled() const { return mDisabled; }

--- a/layout/style/ServoStyleSheet.cpp
+++ b/layout/style/ServoStyleSheet.cpp
@@ -19,33 +19,21 @@ ServoStyleSheet::ServoStyleSheet(css::Sh
 }
 
 ServoStyleSheet::~ServoStyleSheet()
 {
   DropSheet();
 }
 
 bool
-ServoStyleSheet::IsApplicable() const
-{
-  return !mDisabled && mComplete;
-}
-
-bool
 ServoStyleSheet::HasRules() const
 {
   return mSheet && Servo_StyleSheet_HasRules(RawSheet());
 }
 
-nsIDocument*
-ServoStyleSheet::GetOwningDocument() const
-{
-  return mDocument;
-}
-
 void
 ServoStyleSheet::SetOwningDocument(nsIDocument* aDocument)
 {
   // XXXheycam: Traverse to child ServoStyleSheets to set this, like
   // CSSStyleSheet::SetOwningDocument does.
 
   mDocument = aDocument;
 }

--- a/layout/style/ServoStyleSheet.h
+++ b/layout/style/ServoStyleSheet.h
@@ -25,20 +25,18 @@ class ServoStyleSheet : public StyleShee
 public:
   ServoStyleSheet(css::SheetParsingMode aParsingMode,
                   CORSMode aCORSMode,
                   net::ReferrerPolicy aReferrerPolicy,
                   const dom::SRIMetadata& aIntegrity);
 
   NS_INLINE_DECL_REFCOUNTING(ServoStyleSheet)
 
-  bool IsApplicable() const;
   bool HasRules() const;
 
-  nsIDocument* GetOwningDocument() const;
   void SetOwningDocument(nsIDocument* aDocument);
 
   ServoStyleSheet* GetParentSheet() const;
   void AppendStyleSheet(ServoStyleSheet* aSheet);
 
   MOZ_MUST_USE nsresult ParseSheet(const nsAString& aInput,
                                    nsIURI* aSheetURI,
                                    nsIURI* aBaseURI,

--- a/layout/style/StyleSheet.h
+++ b/layout/style/StyleSheet.h
@@ -36,18 +36,16 @@ public:
   void SetOwningNode(nsINode* aOwningNode)
   {
     mOwningNode = aOwningNode;
   }
 
   css::SheetParsingMode ParsingMode() { return mParsingMode; }
   mozilla::dom::CSSStyleSheetParsingMode ParsingModeDOM();
 
-  nsINode* GetOwnerNode() const { return mOwningNode; }
-
   // The document this style sheet is associated with.  May be null
   nsIDocument* GetDocument() const { return mDocument; }
 
   /**
    * Whether the sheet is complete.
    */
   bool IsComplete() const;
   void SetComplete();
@@ -70,16 +68,73 @@ public:
   // Only safe to call if the caller has verified that that |this| is of the
   // correct type.
   inline CSSStyleSheet& AsGecko();
   inline ServoStyleSheet& AsServo();
   inline StyleSheetHandle AsHandle();
   inline const CSSStyleSheet& AsGecko() const;
   inline const ServoStyleSheet& AsServo() const;
 
+  inline MozExternalRefCountType AddRef();
+  inline MozExternalRefCountType Release();
+
+  // Whether the sheet is for an inline <style> element.
+  inline bool IsInline() const;
+
+  inline nsIURI* GetSheetURI() const;
+  /* Get the URI this sheet was originally loaded from, if any.  Can
+     return null */
+  inline nsIURI* GetOriginalURI() const;
+  inline nsIURI* GetBaseURI() const;
+  /**
+   * SetURIs must be called on all sheets before parsing into them.
+   * SetURIs may only be called while the sheet is 1) incomplete and 2)
+   * has no rules in it
+   */
+  inline void SetURIs(nsIURI* aSheetURI, nsIURI* aOriginalSheetURI,
+                      nsIURI* aBaseURI);
+
+  /**
+   * Whether the sheet is applicable.  A sheet that is not applicable
+   * should never be inserted into a style set.  A sheet may not be
+   * applicable for a variety of reasons including being disabled and
+   * being incomplete.
+   */
+  inline bool IsApplicable() const;
+  inline bool HasRules() const;
+
+  // style sheet owner info
+  nsIDocument* GetOwningDocument() const { return mDocument; }
+  inline void SetOwningDocument(nsIDocument* aDocument);
+  nsINode* GetOwnerNode() const { return mOwningNode; }
+  inline StyleSheet* GetParentSheet() const;
+
+  inline void AppendStyleSheet(StyleSheet* aSheet);
+
+  // Principal() never returns a null pointer.
+  inline nsIPrincipal* Principal() const;
+  /**
+   * SetPrincipal should be called on all sheets before parsing into them.
+   * This can only be called once with a non-null principal.  Calling this with
+   * a null pointer is allowed and is treated as a no-op.
+   */
+  inline void SetPrincipal(nsIPrincipal* aPrincipal);
+
+  // Get this style sheet's CORS mode
+  inline CORSMode GetCORSMode() const;
+  // Get this style sheet's Referrer Policy
+  inline net::ReferrerPolicy GetReferrerPolicy() const;
+  // Get this style sheet's integrity metadata
+  inline void GetIntegrity(dom::SRIMetadata& aResult) const;
+
+  inline size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const;
+#ifdef DEBUG
+  inline void List(FILE* aOut = stdout, int32_t aIndex = 0) const;
+#endif
+
 protected:
   nsIDocument*          mDocument; // weak ref; parents maintain this for their children
   nsINode*              mOwningNode; // weak ref
 
   // mParsingMode controls access to nonstandard style constructs that
   // are not safe for use on the public Web but necessary in UA sheets
   // and/or useful in user sheets.
   css::SheetParsingMode mParsingMode;

--- a/layout/style/StyleSheetInfo.cpp
+++ b/layout/style/StyleSheetInfo.cpp
@@ -40,34 +40,9 @@ StyleSheetInfo::StyleSheetInfo(const Sty
   , mIntegrity(aCopy.mIntegrity)
   , mComplete(aCopy.mComplete)
 #ifdef DEBUG
   , mPrincipalSet(aCopy.mPrincipalSet)
 #endif
 {
 }
 
-void
-StyleSheetInfo::SetURIs(nsIURI* aSheetURI,
-                        nsIURI* aOriginalSheetURI,
-                        nsIURI* aBaseURI)
-{
-  NS_PRECONDITION(aSheetURI && aBaseURI, "null ptr");
-
-  mSheetURI = aSheetURI;
-  mOriginalSheetURI = aOriginalSheetURI;
-  mBaseURI = aBaseURI;
-}
-
-void
-StyleSheetInfo::SetPrincipal(nsIPrincipal* aPrincipal)
-{
-  NS_PRECONDITION(!mPrincipalSet, "Should only set principal once");
-
-  if (aPrincipal) {
-    mPrincipal = aPrincipal;
-#ifdef DEBUG
-    mPrincipalSet = true;
-#endif
-  }
-}
-
 } // namespace mozilla

--- a/layout/style/StyleSheetInfo.h
+++ b/layout/style/StyleSheetInfo.h
@@ -6,22 +6,23 @@
 
 #ifndef mozilla_StyleSheetInfo_h
 #define mozilla_StyleSheetInfo_h
 
 #include "mozilla/dom/SRIMetadata.h"
 #include "mozilla/net/ReferrerPolicy.h"
 #include "mozilla/CORSMode.h"
 
+#include "nsIURI.h"
+
 namespace mozilla {
 class CSSStyleSheet;
 } // namespace mozilla
 class nsCSSRuleProcessor;
 class nsIPrincipal;
-class nsIURI;
 
 namespace mozilla {
 
 /**
  * Superclass for data common to CSSStyleSheetInner and ServoStyleSheet.
  */
 class StyleSheetInfo
 {
@@ -30,31 +31,16 @@ public:
   friend class ::nsCSSRuleProcessor;
   typedef net::ReferrerPolicy ReferrerPolicy;
 
   StyleSheetInfo(CORSMode aCORSMode,
                  ReferrerPolicy aReferrerPolicy,
                  const dom::SRIMetadata& aIntegrity);
   StyleSheetInfo(const StyleSheetInfo& aCopy);
 
-  nsIURI* GetSheetURI() const { return mSheetURI; }
-  nsIURI* GetOriginalURI() const { return mOriginalSheetURI; }
-  nsIURI* GetBaseURI() const { return mBaseURI; }
-  void SetURIs(nsIURI* aSheetURI, nsIURI* aOriginalSheetURI, nsIURI* aBaseURI);
-
-  // Whether the sheet is for an inline <style> element.
-  bool IsInline() const { return !mOriginalSheetURI; }
-
-  nsIPrincipal* Principal() const { return mPrincipal; }
-  void SetPrincipal(nsIPrincipal* aPrincipal);
-
-  CORSMode GetCORSMode() const { return mCORSMode; }
-  net::ReferrerPolicy GetReferrerPolicy() const { return mReferrerPolicy; }
-  void GetIntegrity(dom::SRIMetadata& aResult) const { aResult = mIntegrity; }
-
 protected:
   nsCOMPtr<nsIURI>       mSheetURI; // for error reports, etc.
   nsCOMPtr<nsIURI>       mOriginalSheetURI;  // for GetHref.  Can be null.
   nsCOMPtr<nsIURI>       mBaseURI; // for resolving relative URIs
   nsCOMPtr<nsIPrincipal> mPrincipal;
   CORSMode               mCORSMode;
   // The Referrer Policy of a stylesheet is used for its child sheets, so it is
   // stored here.

--- a/layout/style/StyleSheetInlines.h
+++ b/layout/style/StyleSheetInlines.h
@@ -2,16 +2,17 @@
 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #ifndef mozilla_StyleSheetInlines_h
 #define mozilla_StyleSheetInlines_h
 
+#include "mozilla/TypeTraits.h"
 #include "mozilla/ServoStyleSheet.h"
 #include "mozilla/CSSStyleSheet.h"
 
 namespace mozilla {
 
 CSSStyleSheet&
 StyleSheet::AsGecko()
 {
@@ -44,11 +45,158 @@ StyleSheet::AsGecko() const
 
 const ServoStyleSheet&
 StyleSheet::AsServo() const
 {
   MOZ_ASSERT(IsServo());
   return *static_cast<const ServoStyleSheet*>(this);
 }
 
+#define FORWARD_CONCRETE(method_, geckoargs_, servoargs_) \
+  static_assert(!IsSame<decltype(&StyleSheet::method_), \
+                        decltype(&CSSStyleSheet::method_)>::value, \
+                "CSSStyleSheet should define its own " #method_); \
+  static_assert(!IsSame<decltype(&StyleSheet::method_), \
+                        decltype(&ServoStyleSheet::method_)>::value, \
+                "ServoStyleSheet should define its own " #method_); \
+  if (IsServo()) { \
+    return AsServo().method_ servoargs_; \
+  } \
+  return AsGecko().method_ geckoargs_;
+
+#define FORWARD(method_, args_) FORWARD_CONCRETE(method_, args_, args_)
+
+MozExternalRefCountType
+StyleSheet::AddRef()
+{
+  FORWARD(AddRef, ())
+}
+
+MozExternalRefCountType
+StyleSheet::Release()
+{
+  FORWARD(Release, ())
+}
+
+bool
+StyleSheet::IsInline() const
+{
+  return !SheetInfo().mOriginalSheetURI;
+}
+
+nsIURI*
+StyleSheet::GetSheetURI() const
+{
+  return SheetInfo().mSheetURI;
+}
+
+nsIURI*
+StyleSheet::GetOriginalURI() const
+{
+  return SheetInfo().mOriginalSheetURI;
+}
+
+nsIURI*
+StyleSheet::GetBaseURI() const
+{
+  return SheetInfo().mBaseURI;
+}
+
+void
+StyleSheet::SetURIs(nsIURI* aSheetURI, nsIURI* aOriginalSheetURI,
+                    nsIURI* aBaseURI)
+{
+  NS_PRECONDITION(aSheetURI && aBaseURI, "null ptr");
+  StyleSheetInfo& info = SheetInfo();
+  MOZ_ASSERT(!HasRules() && !info.mComplete,
+             "Can't call SetURIs on sheets that are complete or have rules");
+  info.mSheetURI = aSheetURI;
+  info.mOriginalSheetURI = aOriginalSheetURI;
+  info.mBaseURI = aBaseURI;
+}
+
+bool
+StyleSheet::IsApplicable() const
+{
+  return !mDisabled && SheetInfo().mComplete;
+}
+
+bool
+StyleSheet::HasRules() const
+{
+  FORWARD(HasRules, ())
+}
+
+void
+StyleSheet::SetOwningDocument(nsIDocument* aDocument)
+{
+  FORWARD(SetOwningDocument, (aDocument))
+}
+
+StyleSheet*
+StyleSheet::GetParentSheet() const
+{
+  FORWARD(GetParentSheet, ())
+}
+
+void
+StyleSheet::AppendStyleSheet(StyleSheet* aSheet)
+{
+  FORWARD_CONCRETE(AppendStyleSheet, (&aSheet->AsGecko()), (&aSheet->AsServo()))
+}
+
+nsIPrincipal*
+StyleSheet::Principal() const
+{
+  return SheetInfo().mPrincipal;
+}
+
+void
+StyleSheet::SetPrincipal(nsIPrincipal* aPrincipal)
+{
+  StyleSheetInfo& info = SheetInfo();
+  NS_PRECONDITION(!info.mPrincipalSet, "Should only set principal once");
+  if (aPrincipal) {
+    info.mPrincipal = aPrincipal;
+#ifdef DEBUG
+    info.mPrincipalSet = true;
+#endif
+  }
+}
+
+CORSMode
+StyleSheet::GetCORSMode() const
+{
+  return SheetInfo().mCORSMode;
+}
+
+net::ReferrerPolicy
+StyleSheet::GetReferrerPolicy() const
+{
+  return SheetInfo().mReferrerPolicy;
+}
+
+void
+StyleSheet::GetIntegrity(dom::SRIMetadata& aResult) const
+{
+  aResult = SheetInfo().mIntegrity;
+}
+
+size_t
+StyleSheet::SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const
+{
+  FORWARD(SizeOfIncludingThis, (aMallocSizeOf))
+}
+
+#ifdef DEBUG
+void
+StyleSheet::List(FILE* aOut, int32_t aIndex) const
+{
+  FORWARD(List, (aOut, aIndex))
+}
+#endif
+
+#undef FORWARD
+#undef FORWARD_CONCRETE
+
 }
 
 #endif // mozilla_StyleSheetInlines_h