diff --git a/gfx/public/nsITheme.h b/gfx/public/nsITheme.h
index 8c1ee6908d5c..94f108bb8449 100644
--- a/gfx/public/nsITheme.h
+++ b/gfx/public/nsITheme.h
@@ -59,7 +59,8 @@ class nsIAtom;
 // IID for the nsITheme interface
 // {887e8902-db6b-41b4-8481-a80f49c5a93a}
  #define NS_ITHEME_IID     \
-{ 0x23db7c13, 0x873d, 0x4fb5, { 0xaf, 0x29, 0xc1, 0xe9, 0xed, 0x91, 0x23, 0xf9 } }
+{ 0x887e8902, 0xdb6b, 0x41b4, { 0x84, 0x81, 0xa8, 0x0f, 0x49, 0xc5, 0xa9, 0x3a } }
+
 // {D930E29B-6909-44e5-AB4B-AF10D6923705}
 #define NS_THEMERENDERER_CID \
 { 0xd930e29b, 0x6909, 0x44e5, { 0xab, 0x4b, 0xaf, 0x10, 0xd6, 0x92, 0x37, 0x5 } }
@@ -138,18 +139,7 @@ public:
                                   nsIntSize* aResult,
                                   PRBool* aIsOverridable)=0;
 
-
-  enum Transparency {
-    eOpaque = 0,
-    eTransparent,
-    eUnknownTransparency
-  };
-
-  /**
-   * Returns what we know about the transparency of the widget.
-   */
-  virtual Transparency GetWidgetTransparency(nsIFrame* aFrame, PRUint8 aWidgetType)
-  { return eUnknownTransparency; }
+  virtual nsTransparencyMode GetWidgetTransparency(PRUint8 aWidgetType)=0;
 
   NS_IMETHOD WidgetStateChanged(nsIFrame* aFrame, PRUint8 aWidgetType, 
                                 nsIAtom* aAttribute, PRBool* aShouldRepaint)=0;
diff --git a/layout/base/nsDisplayList.cpp b/layout/base/nsDisplayList.cpp
index b7a4e3cdf8e8..0e6afcaecec4 100644
--- a/layout/base/nsDisplayList.cpp
+++ b/layout/base/nsDisplayList.cpp
@@ -675,7 +675,7 @@ PRBool
 nsDisplayBackground::IsOpaque(nsDisplayListBuilder* aBuilder) {
   // theme background overrides any other background
   if (mIsThemed)
-    return mThemeTransparency == nsITheme::eOpaque;
+    return PR_FALSE;
 
   nsStyleContext *bgSC;
   if (!nsCSSRendering::FindBackground(mFrame->PresContext(), mFrame, &bgSC))
diff --git a/layout/base/nsDisplayList.h b/layout/base/nsDisplayList.h
index 22fffe4d3d11..65a06e2689d6 100644
--- a/layout/base/nsDisplayList.h
+++ b/layout/base/nsDisplayList.h
@@ -1257,7 +1257,7 @@ private:
 class nsDisplayBackground : public nsDisplayItem {
 public:
   nsDisplayBackground(nsIFrame* aFrame) : nsDisplayItem(aFrame) {
-    mIsThemed = mFrame->IsThemed(&mThemeTransparency);
+    mIsThemed = mFrame->IsThemed();
     MOZ_COUNT_CTOR(nsDisplayBackground);
   }
 #ifdef NS_BUILD_REFCNT_LOGGING
@@ -1278,9 +1278,8 @@ public:
   virtual void Paint(nsDisplayListBuilder* aBuilder, nsIRenderingContext* aCtx);
   NS_DISPLAY_DECL_NAME("Background")
 private:
-  /* Used to cache mFrame->IsThemed() since it isn't a cheap call */
-  PRPackedBool mIsThemed;
-  nsITheme::Transparency mThemeTransparency;
+    /* Used to cache mFrame->IsThemed() since it isn't a cheap call */
+    PRPackedBool mIsThemed;
 };
 
 /**
diff --git a/layout/base/nsLayoutUtils.cpp b/layout/base/nsLayoutUtils.cpp
index 10856c2400ad..97ecc10ad774 100644
--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -3216,11 +3216,9 @@ nsLayoutUtils::GetFrameTransparency(nsIFrame* aBackgroundFrame,
   if (HasNonZeroCorner(aCSSRootFrame->GetStyleContext()->GetStyleBorder()->mBorderRadius))
     return eTransparencyTransparent;
 
-  nsITheme::Transparency transparency;
+  nsTransparencyMode transparency;
   if (aCSSRootFrame->IsThemed(&transparency))
-    return transparency == nsITheme::eTransparent
-         ? eTransparencyTransparent
-         : eTransparencyOpaque;
+    return transparency;
 
   if (aCSSRootFrame->GetStyleDisplay()->mAppearance == NS_THEME_WIN_GLASS)
     return eTransparencyGlass;
diff --git a/layout/generic/nsIFrame.h b/layout/generic/nsIFrame.h
index bf4c4de363b4..8e289d79652d 100644
--- a/layout/generic/nsIFrame.h
+++ b/layout/generic/nsIFrame.h
@@ -997,20 +997,19 @@ public:
    */
   virtual nscolor GetCaretColorAt(PRInt32 aOffset);
 
- 
-  PRBool IsThemed(nsITheme::Transparency* aTransparencyState = nsnull) {
-    return IsThemed(GetStyleDisplay(), aTransparencyState);
+  PRBool IsThemed(nsTransparencyMode* aTransparencyMode = nsnull) {
+    return IsThemed(GetStyleDisplay(), aTransparencyMode);
   }
   PRBool IsThemed(const nsStyleDisplay* aDisp,
-                  nsITheme::Transparency* aTransparencyState = nsnull) {
+                  nsTransparencyMode* aTransparencyMode = nsnull) {
     if (!aDisp->mAppearance)
       return PR_FALSE;
     nsPresContext* pc = PresContext();
     nsITheme *theme = pc->GetTheme();
     if(!theme || !theme->ThemeSupportsWidget(pc, this, aDisp->mAppearance))
       return PR_FALSE;
-    if (aTransparencyState) {
-      *aTransparencyState = theme->GetWidgetTransparency(this, aDisp->mAppearance);
+    if (aTransparencyMode) {
+      *aTransparencyMode = theme->GetWidgetTransparency(aDisp->mAppearance);
     }
     return PR_TRUE;
   }
diff --git a/widget/src/cocoa/nsNativeThemeCocoa.h b/widget/src/cocoa/nsNativeThemeCocoa.h
index 60a57c4304d9..10902f12bc9d 100644
--- a/widget/src/cocoa/nsNativeThemeCocoa.h
+++ b/widget/src/cocoa/nsNativeThemeCocoa.h
@@ -90,7 +90,7 @@ public:
   PRBool WidgetIsContainer(PRUint8 aWidgetType);
   PRBool ThemeDrawsFocusForWidget(nsPresContext* aPresContext, nsIFrame* aFrame, PRUint8 aWidgetType);
   PRBool ThemeNeedsComboboxDropmarker();
-  virtual Transparency GetWidgetTransparency(nsIFrame* aFrame, PRUint8 aWidgetType);
+  virtual nsTransparencyMode GetWidgetTransparency(PRUint8 aWidgetType);
 
 protected:  
 
diff --git a/widget/src/cocoa/nsNativeThemeCocoa.mm b/widget/src/cocoa/nsNativeThemeCocoa.mm
index f89f3922f627..b4774ceee90e 100644
--- a/widget/src/cocoa/nsNativeThemeCocoa.mm
+++ b/widget/src/cocoa/nsNativeThemeCocoa.mm
@@ -2480,12 +2480,12 @@ nsNativeThemeCocoa::ThemeNeedsComboboxDropmarker()
   return PR_FALSE;
 }
 
-nsITheme::Transparency
-nsNativeThemeCocoa::GetWidgetTransparency(nsIFrame* aFrame, PRUint8 aWidgetType)
+nsTransparencyMode
+nsNativeThemeCocoa::GetWidgetTransparency(PRUint8 aWidgetType)
 {
   if (aWidgetType == NS_THEME_MENUPOPUP ||
       aWidgetType == NS_THEME_TOOLTIP)
-    return eTransparent;
+    return eTransparencyTransparent;
 
-  return eUnknownTransparency;
+  return eTransparencyOpaque;
 }
diff --git a/widget/src/gtk2/nsNativeThemeGTK.cpp b/widget/src/gtk2/nsNativeThemeGTK.cpp
index 871ee9bc7c06..35ef4db49048 100644
--- a/widget/src/gtk2/nsNativeThemeGTK.cpp
+++ b/widget/src/gtk2/nsNativeThemeGTK.cpp
@@ -1342,3 +1342,9 @@ nsNativeThemeGTK::ThemeNeedsComboboxDropmarker()
 {
   return PR_FALSE;
 }
+
+nsTransparencyMode
+nsNativeThemeGTK::GetWidgetTransparency(PRUint8 aWidgetType)
+{
+  return eTransparencyOpaque;
+}
diff --git a/widget/src/gtk2/nsNativeThemeGTK.h b/widget/src/gtk2/nsNativeThemeGTK.h
index 704457bfd4eb..f708c945756d 100644
--- a/widget/src/gtk2/nsNativeThemeGTK.h
+++ b/widget/src/gtk2/nsNativeThemeGTK.h
@@ -92,6 +92,8 @@ public:
 
   PRBool ThemeNeedsComboboxDropmarker();
 
+  virtual nsTransparencyMode GetWidgetTransparency(PRUint8 aWidgetType);
+
   nsNativeThemeGTK();
   virtual ~nsNativeThemeGTK();
 
diff --git a/widget/src/qt/nsNativeThemeQt.cpp b/widget/src/qt/nsNativeThemeQt.cpp
index 43a46db802cd..f89102aaad10 100644
--- a/widget/src/qt/nsNativeThemeQt.cpp
+++ b/widget/src/qt/nsNativeThemeQt.cpp
@@ -627,6 +627,12 @@ nsNativeThemeQt::ThemeNeedsComboboxDropmarker()
     return PR_TRUE;
 }
 
+nsTransparencyMode
+nsNativeThemeQt::GetWidgetTransparency(PRUint8 aWidgetType)
+{
+  return eTransparencyOpaque;
+}
+
 void
 nsNativeThemeQt::InitButtonStyle(PRUint8 aWidgetType,
                                  nsIFrame* aFrame,
diff --git a/widget/src/qt/nsNativeThemeQt.h b/widget/src/qt/nsNativeThemeQt.h
index 86fce2525a7a..4b69c0004634 100644
--- a/widget/src/qt/nsNativeThemeQt.h
+++ b/widget/src/qt/nsNativeThemeQt.h
@@ -99,6 +99,8 @@ public:
 
   PRBool ThemeNeedsComboboxDropmarker();
 
+  virtual nsTransparencyMode GetWidgetTransparency(PRUint8 aWidgetType);
+
   nsNativeThemeQt();
   virtual ~nsNativeThemeQt();
 
diff --git a/widget/src/windows/nsNativeThemeWin.cpp b/widget/src/windows/nsNativeThemeWin.cpp
index 5b306c98e3c4..fdb62ece2154 100644
--- a/widget/src/windows/nsNativeThemeWin.cpp
+++ b/widget/src/windows/nsNativeThemeWin.cpp
@@ -397,13 +397,6 @@ nsNativeThemeWin::IsMenuActive(nsIFrame *aFrame, PRUint8 aWidgetType)
   return CheckBooleanAttr(aFrame, nsWidgetAtoms::mozmenuactive);
 }
 
-/**
- * aPart is filled in with the UXTheme part code. On return, values > 0
- * are the actual UXTheme part code; -1 means the widget will be drawn by
- * us; 0 means that we should use part code 0, which isn't a real part code
- * but elicits some kind of default behaviour from UXTheme when drawing
- * (but isThemeBackgroundPartiallyTransparent may not work).
- */
 nsresult 
 nsNativeThemeWin::GetThemePartAndState(nsIFrame* aFrame, PRUint8 aWidgetType, 
                                        PRInt32& aPart, PRInt32& aState)
@@ -1783,28 +1776,10 @@ nsNativeThemeWin::ThemeNeedsComboboxDropmarker()
   return PR_TRUE;
 }
 
-nsITheme::Transparency
-nsNativeThemeWin::GetWidgetTransparency(nsIFrame* aFrame, PRUint8 aWidgetType)
+nsTransparencyMode
+nsNativeThemeWin::GetWidgetTransparency(PRUint8 aWidgetType)
 {
-  HANDLE theme = GetTheme(aWidgetType);
-  // For the classic theme we don't really have a way of knowing
-  if (!theme)
-    return eUnknownTransparency;
-
-  PRInt32 part, state;
-  nsresult rv = GetThemePartAndState(aFrame, aWidgetType, part, state);
-  // Fail conservatively
-  NS_ENSURE_SUCCESS(rv, eUnknownTransparency);
-
-  if (part <= 0) {
-    // Not a real part code, so isThemeBackgroundPartiallyTransparent may
-    // not work, so don't call it.
-    return eUnknownTransparency;
-  }
-
-  if (nsUXThemeData::isThemeBackgroundPartiallyTransparent(theme, part, state))
-    return eTransparent;
-  return eOpaque;
+  return eTransparencyOpaque;
 }
 
 /* Windows 9x/NT/2000/Classic XP Theme Support */
diff --git a/widget/src/windows/nsNativeThemeWin.h b/widget/src/windows/nsNativeThemeWin.h
index 2a91c96ec178..efb6393511bc 100644
--- a/widget/src/windows/nsNativeThemeWin.h
+++ b/widget/src/windows/nsNativeThemeWin.h
@@ -78,7 +78,7 @@ public:
                                   nsIntSize* aResult,
                                   PRBool* aIsOverridable);
 
-  virtual Transparency GetWidgetTransparency(nsIFrame* aFrame, PRUint8 aWidgetType);
+  virtual nsTransparencyMode GetWidgetTransparency(PRUint8 aWidgetType);
 
   NS_IMETHOD WidgetStateChanged(nsIFrame* aFrame, PRUint8 aWidgetType, 
                                 nsIAtom* aAttribute, PRBool* aShouldRepaint);
diff --git a/widget/src/windows/nsUXThemeData.cpp b/widget/src/windows/nsUXThemeData.cpp
index 4df110ebf6f4..77abcdad3a82 100644
--- a/widget/src/windows/nsUXThemeData.cpp
+++ b/widget/src/windows/nsUXThemeData.cpp
@@ -83,7 +83,6 @@ nsUXThemeData::GetThemeMarginsPtr nsUXThemeData::getThemeMargins = NULL;
 nsUXThemeData::IsAppThemedPtr nsUXThemeData::isAppThemed = NULL;
 nsUXThemeData::GetCurrentThemeNamePtr nsUXThemeData::getCurrentThemeName = NULL;
 nsUXThemeData::GetThemeSysColorPtr nsUXThemeData::getThemeSysColor = NULL;
-nsUXThemeData::IsThemeBackgroundPartiallyTransparentPtr nsUXThemeData::isThemeBackgroundPartiallyTransparent = NULL;
 
 #if MOZ_WINSDK_TARGETVER >= MOZ_NTDDI_LONGHORN
 nsUXThemeData::DwmExtendFrameIntoClientAreaProc nsUXThemeData::dwmExtendFrameIntoClientAreaPtr = NULL;
@@ -125,7 +124,6 @@ nsUXThemeData::Initialize()
     isAppThemed = (IsAppThemedPtr)GetProcAddress(sThemeDLL, "IsAppThemed");
     getCurrentThemeName = (GetCurrentThemeNamePtr)GetProcAddress(sThemeDLL, "GetCurrentThemeName");
     getThemeSysColor = (GetThemeSysColorPtr)GetProcAddress(sThemeDLL, "GetThemeSysColor");
-    isThemeBackgroundPartiallyTransparent = (IsThemeBackgroundPartiallyTransparentPtr)GetProcAddress(sThemeDLL, "IsThemeBackgroundPartiallyTransparent");
   }
 #if MOZ_WINSDK_TARGETVER >= MOZ_NTDDI_LONGHORN
    sDwmDLL = ::LoadLibraryW(kDwmLibraryName);
diff --git a/widget/src/windows/nsUXThemeData.h b/widget/src/windows/nsUXThemeData.h
index 620a0dbef6c2..27efc5a9617c 100644
--- a/widget/src/windows/nsUXThemeData.h
+++ b/widget/src/windows/nsUXThemeData.h
@@ -153,7 +153,6 @@ public:
                                                   LPWSTR pszColorBuff, int cchMaxColorChars,
                                                   LPWSTR pszSizeBuff, int cchMaxSizeChars);
   typedef COLORREF (WINAPI*GetThemeSysColorPtr)(HANDLE hTheme, int iColorID);
-  typedef BOOL (WINAPI*IsThemeBackgroundPartiallyTransparentPtr)(HANDLE hTheme, int iPartId, int iStateId);
 
   static OpenThemeDataPtr openTheme;
   static CloseThemeDataPtr closeTheme;
@@ -168,7 +167,6 @@ public:
   static IsAppThemedPtr isAppThemed;
   static GetCurrentThemeNamePtr getCurrentThemeName;
   static GetThemeSysColorPtr getThemeSysColor;
-  static IsThemeBackgroundPartiallyTransparentPtr isThemeBackgroundPartiallyTransparent;
 
 #if MOZ_WINSDK_TARGETVER >= MOZ_NTDDI_LONGHORN
   // dwmapi.dll function typedefs and declarations