--- a/layout/style/moz.build
+++ b/layout/style/moz.build
@@ -50,17 +50,16 @@ EXPORTS += [
     'nsCSSRuleProcessor.h',
     'nsCSSScanner.h',
     'nsCSSValue.h',
     'nsDOMCSSAttrDeclaration.h',
     'nsDOMCSSDeclaration.h',
     'nsDOMCSSRGBColor.h',
     'nsICSSDeclaration.h',
     'nsICSSLoaderObserver.h',
-    'nsICSSPseudoComparator.h',
     'nsICSSStyleRuleDOMWrapper.h',
     'nsIStyleRule.h',
     'nsIStyleRuleProcessor.h',
     'nsLayoutStylesheetCache.h',
     'nsMediaFeatures.h',
     'nsMediaList.h',
     'nsRuleData.h',
     'nsRuleNode.h',

--- a/layout/style/nsCSSRuleProcessor.cpp
+++ b/layout/style/nsCSSRuleProcessor.cpp
@@ -11,17 +11,16 @@
 
 #include "nsCSSRuleProcessor.h"
 
 #include "nsAutoPtr.h"
 #include "nsRuleProcessorData.h"
 #include <algorithm>
 #include "nsAtom.h"
 #include "PLDHashTable.h"
-#include "nsICSSPseudoComparator.h"
 #include "mozilla/MemoryReporting.h"
 #include "mozilla/css/ImportRule.h"
 #include "mozilla/css/StyleRule.h"
 #include "mozilla/css/GroupRule.h"
 #include "nsIDocument.h"
 #include "nsPresContext.h"
 #include "nsGkAtoms.h"
 #include "nsUnicharUtils.h"

deleted file mode 100644
--- a/layout/style/nsICSSPseudoComparator.h
+++ /dev/null
@@ -1,19 +0,0 @@
-/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* 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/. */
-
-/* internal interface for implementing complex pseudo-classes */
-
-#ifndef nsICSSPseudoComparator_h___
-#define nsICSSPseudoComparator_h___
-
-struct nsCSSSelector;
-
-class nsICSSPseudoComparator
-{
-public:
-  virtual bool PseudoMatches(nsCSSSelector* aSelector)=0;
-};
-
-#endif /* nsICSSPseudoComparator_h___ */

--- a/layout/xul/tree/nsTreeBodyFrame.cpp
+++ b/layout/xul/tree/nsTreeBodyFrame.cpp
@@ -4470,28 +4470,21 @@ nsTreeBodyFrame::ThumbMoved(nsScrollbarF
     UpdateScrollbars(parts);
   }
 }
 
 // The style cache.
 nsStyleContext*
 nsTreeBodyFrame::GetPseudoStyleContext(nsICSSAnonBoxPseudo* aPseudoElement)
 {
-  return mStyleCache.GetStyleContext(this, PresContext(), mContent,
+  return mStyleCache.GetStyleContext(PresContext(), mContent,
                                      mStyleContext, aPseudoElement,
                                      mScratchArray);
 }
 
-// Our comparator for resolving our complex pseudos
-bool
-nsTreeBodyFrame::PseudoMatches(nsCSSSelector* aSelector)
-{
-  return true;
-}
-
 nsIContent*
 nsTreeBodyFrame::GetBaseElement()
 {
   nsIFrame* parent = GetParent();
   while (parent) {
     nsIContent* content = parent->GetContent();
     if (content) {
       dom::NodeInfo* ni = content->NodeInfo();

--- a/layout/xul/tree/nsTreeBodyFrame.h
+++ b/layout/xul/tree/nsTreeBodyFrame.h
@@ -6,17 +6,16 @@
 #ifndef nsTreeBodyFrame_h
 #define nsTreeBodyFrame_h
 
 #include "mozilla/AtomArray.h"
 #include "mozilla/Attributes.h"
 
 #include "nsLeafBoxFrame.h"
 #include "nsITreeView.h"
-#include "nsICSSPseudoComparator.h"
 #include "nsIScrollbarMediator.h"
 #include "nsITimer.h"
 #include "nsIReflowCallback.h"
 #include "nsTArray.h"
 #include "nsTreeStyleCache.h"
 #include "nsTreeColumns.h"
 #include "nsDataHashtable.h"
 #include "imgIRequest.h"
@@ -44,17 +43,16 @@ struct nsTreeImageCacheEntry
 
   nsCOMPtr<imgIRequest> request;
   nsCOMPtr<imgINotificationObserver> listener;
 };
 
 // The actual frame that paints the cells and rows.
 class nsTreeBodyFrame final
   : public nsLeafBoxFrame
-  , public nsICSSPseudoComparator
   , public nsIScrollbarMediator
   , public nsIReflowCallback
 {
   typedef mozilla::layout::ScrollbarActivity ScrollbarActivity;
   typedef mozilla::image::DrawResult DrawResult;
 
 public:
   explicit nsTreeBodyFrame(nsStyleContext* aContext);
@@ -127,19 +125,16 @@ public:
   virtual nsSize GetXULMinSize(nsBoxLayoutState& aBoxLayoutState) override;
   virtual void SetXULBounds(nsBoxLayoutState& aBoxLayoutState, const nsRect& aRect,
                             bool aRemoveOverflowArea = false) override;
 
   // nsIReflowCallback
   virtual bool ReflowFinished() override;
   virtual void ReflowCallbackCanceled() override;
 
-  // nsICSSPseudoComparator
-  virtual bool PseudoMatches(nsCSSSelector* aSelector) override;
-
   // nsIScrollbarMediator
   virtual void ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirection,
                             nsIScrollbarMediator::ScrollSnapMode aSnap
                               = nsIScrollbarMediator::DISABLE_SNAP) override;
   virtual void ScrollByWhole(nsScrollbarFrame* aScrollbar, int32_t aDirection,
                              nsIScrollbarMediator::ScrollSnapMode aSnap
                                = nsIScrollbarMediator::DISABLE_SNAP) override;
   virtual void ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection,

--- a/layout/xul/tree/nsTreeStyleCache.cpp
+++ b/layout/xul/tree/nsTreeStyleCache.cpp
@@ -27,18 +27,17 @@ nsTreeStyleCache::Transition::Hash() con
   uint32_t hb = mState << 16;
   uint32_t lb = (NS_PTR_TO_UINT32(mInputSymbol.get()) << 16) >> 16;
   return hb+lb;
 }
 
 
 // The style context cache impl
 nsStyleContext*
-nsTreeStyleCache::GetStyleContext(nsICSSPseudoComparator* aComparator,
-                                  nsPresContext* aPresContext,
+nsTreeStyleCache::GetStyleContext(nsPresContext* aPresContext,
                                   nsIContent* aContent,
                                   nsStyleContext* aContext,
                                   nsICSSAnonBoxPseudo* aPseudoElement,
                                   const AtomArray & aInputWord)
 {
   MOZ_ASSERT(nsCSSAnonBoxes::IsTreePseudoElement(aPseudoElement));
 
   uint32_t count = aInputWord.Length();

--- a/layout/xul/tree/nsTreeStyleCache.h
+++ b/layout/xul/tree/nsTreeStyleCache.h
@@ -5,17 +5,16 @@
 
 #ifndef nsTreeStyleCache_h__
 #define nsTreeStyleCache_h__
 
 #include "mozilla/AtomArray.h"
 #include "mozilla/Attributes.h"
 #include "nsAutoPtr.h"
 #include "nsCOMArray.h"
-#include "nsICSSPseudoComparator.h"
 #include "nsRefPtrHashtable.h"
 #include "nsStyleContext.h"
 
 class nsTreeStyleCache
 {
 public:
   nsTreeStyleCache()
     : mNextState(0)
@@ -29,18 +28,17 @@ public:
 
   void Clear()
   {
     mTransitionTable = nullptr;
     mCache = nullptr;
     mNextState = 0;
   }
 
-  nsStyleContext* GetStyleContext(nsICSSPseudoComparator* aComparator,
-                                  nsPresContext* aPresContext,
+  nsStyleContext* GetStyleContext(nsPresContext* aPresContext,
                                   nsIContent* aContent,
                                   nsStyleContext* aContext,
                                   nsICSSAnonBoxPseudo* aPseudoElement,
                                   const mozilla::AtomArray& aInputWord);
 
 protected:
   typedef uint32_t DFAState;