diff --git a/gfx/layers/composite/LayerManagerComposite.cpp b/gfx/layers/composite/LayerManagerComposite.cpp
index 3fdf179aaec4..8caf08830233 100644
--- a/gfx/layers/composite/LayerManagerComposite.cpp
+++ b/gfx/layers/composite/LayerManagerComposite.cpp
@@ -810,10 +810,9 @@ LayerManagerComposite::Render(const nsIntRegion& aInvalidRegion)
   }
 
   // Allow widget to render a custom foreground.
-  mCompositor->GetWidget()->DrawWindowOverlay(this, IntRect(actualBounds.x,
-                                                              actualBounds.y,
-                                                              actualBounds.width,
-                                                              actualBounds.height));
+  mCompositor->GetWidget()->DrawWindowOverlay(
+    this, LayoutDeviceIntRect(actualBounds.x, actualBounds.y,
+                              actualBounds.width, actualBounds.height));
 
   // Debugging
   RenderDebugOverlay(actualBounds);
diff --git a/layout/generic/nsGfxScrollFrame.cpp b/layout/generic/nsGfxScrollFrame.cpp
index a2c6f4e0a3e7..d29b9e35cea9 100644
--- a/layout/generic/nsGfxScrollFrame.cpp
+++ b/layout/generic/nsGfxScrollFrame.cpp
@@ -4928,7 +4928,7 @@ ScrollFrameHelper::AdjustScrollbarRectForResizer(
   else {
     nsPoint offset;
     nsIWidget* widget = aFrame->GetNearestWidget(offset);
-    nsIntRect widgetRect;
+    LayoutDeviceIntRect widgetRect;
     if (!widget || !widget->ShowsResizeIndicator(&widgetRect))
       return;
 
diff --git a/widget/android/nsWindow.cpp b/widget/android/nsWindow.cpp
index 267becc6f8d5..5793c7cfa0c0 100644
--- a/widget/android/nsWindow.cpp
+++ b/widget/android/nsWindow.cpp
@@ -2637,7 +2637,8 @@ nsWindow::DrawWindowUnderlay(LayerManagerComposite* aManager, nsIntRect aRect)
 }
 
 void
-nsWindow::DrawWindowOverlay(LayerManagerComposite* aManager, nsIntRect aRect)
+nsWindow::DrawWindowOverlay(LayerManagerComposite* aManager,
+                            LayoutDeviceIntRect aRect)
 {
     PROFILER_LABEL("nsWindow", "DrawWindowOverlay",
         js::ProfileEntry::Category::GRAPHICS);
diff --git a/widget/android/nsWindow.h b/widget/android/nsWindow.h
index 2cd4a2f8709d..2c9c3c2a44cc 100644
--- a/widget/android/nsWindow.h
+++ b/widget/android/nsWindow.h
@@ -152,7 +152,7 @@ public:
 
     virtual bool NeedsPaint() override;
     virtual void DrawWindowUnderlay(LayerManagerComposite* aManager, nsIntRect aRect) override;
-    virtual void DrawWindowOverlay(LayerManagerComposite* aManager, nsIntRect aRect) override;
+    virtual void DrawWindowOverlay(LayerManagerComposite* aManager, LayoutDeviceIntRect aRect) override;
 
     virtual mozilla::layers::CompositorParent* NewCompositorParent(int aSurfaceWidth, int aSurfaceHeight) override;
 
diff --git a/widget/cocoa/TextInputHandler.mm b/widget/cocoa/TextInputHandler.mm
index e08c8a0e3b0d..7232b003614c 100644
--- a/widget/cocoa/TextInputHandler.mm
+++ b/widget/cocoa/TextInputHandler.mm
@@ -3316,8 +3316,7 @@ IMEInputHandler::FirstRectForCharacterRange(NSRange& aRange,
   if (!rootWindow || !rootView) {
     return rect;
   }
-  rect = nsCocoaUtils::DevPixelsToCocoaPoints(r.ToUnknownRect(),
-                                              mWidget->BackingScaleFactor());
+  rect = nsCocoaUtils::DevPixelsToCocoaPoints(r, mWidget->BackingScaleFactor());
   rect = [rootView convertRect:rect toView:nil];
   rect.origin = [rootWindow convertBaseToScreen:rect.origin];
 
diff --git a/widget/cocoa/VibrancyManager.mm b/widget/cocoa/VibrancyManager.mm
index bdadb1465f27..33f04a9e283b 100644
--- a/widget/cocoa/VibrancyManager.mm
+++ b/widget/cocoa/VibrancyManager.mm
@@ -32,7 +32,7 @@ VibrancyManager::UpdateVibrantRegion(VibrancyType aType, const nsIntRegion& aReg
   for (size_t i = 0; (iterRect = iter.Next()) || i < viewsToRecycle.Length(); ++i) {
     if (iterRect) {
       NSView* view = nil;
-      NSRect rect = mCoordinateConverter.DevPixelsToCocoaPoints(*iterRect);
+      NSRect rect = mCoordinateConverter.UntypedDevPixelsToCocoaPoints(*iterRect);
       if (i < viewsToRecycle.Length()) {
         view = viewsToRecycle[i];
         [view setFrame:rect];
@@ -72,7 +72,7 @@ VibrancyManager::ClearVibrantRegion(const VibrantRegion& aVibrantRegion) const
 
   nsIntRegionRectIterator iter(aVibrantRegion.region);
   while (const nsIntRect* rect = iter.Next()) {
-    NSRectFill(mCoordinateConverter.DevPixelsToCocoaPoints(*rect));
+    NSRectFill(mCoordinateConverter.UntypedDevPixelsToCocoaPoints(*rect));
   }
 }
 
diff --git a/widget/cocoa/nsChildView.h b/widget/cocoa/nsChildView.h
index 747450a867e8..37683f33857c 100644
--- a/widget/cocoa/nsChildView.h
+++ b/widget/cocoa/nsChildView.h
@@ -403,7 +403,7 @@ public:
   virtual void*           GetNativeData(uint32_t aDataType) override;
   virtual nsresult        ConfigureChildren(const nsTArray<Configuration>& aConfigurations) override;
   virtual LayoutDeviceIntPoint WidgetToScreenOffset() override;
-  virtual bool            ShowsResizeIndicator(nsIntRect* aResizerRect) override;
+  virtual bool            ShowsResizeIndicator(LayoutDeviceIntRect* aResizerRect) override;
 
   static  bool            ConvertStatus(nsEventStatus aStatus)
                           { return aStatus == nsEventStatus_eConsumeNoDefault; }
@@ -487,12 +487,13 @@ public:
   virtual void CleanupWindowEffects() override;
   virtual bool PreRender(LayerManagerComposite* aManager) override;
   virtual void PostRender(LayerManagerComposite* aManager) override;
-  virtual void DrawWindowOverlay(LayerManagerComposite* aManager, nsIntRect aRect) override;
+  virtual void DrawWindowOverlay(LayerManagerComposite* aManager,
+                                 LayoutDeviceIntRect aRect) override;
 
   virtual void UpdateThemeGeometries(const nsTArray<ThemeGeometry>& aThemeGeometries) override;
 
   virtual void UpdateWindowDraggingRegion(const nsIntRegion& aRegion) override;
-  const nsIntRegion& GetDraggableRegion() { return mDraggableRegion; }
+  const LayoutDeviceIntRegion& GetDraggableRegion() { return mDraggableRegion; }
 
   virtual void ReportSwipeStarted(uint64_t aInputBlockId, bool aStartSwipe) override;
 
@@ -524,13 +525,18 @@ public:
   nsIntPoint        CocoaPointsToDevPixels(const NSPoint& aPt) const {
     return nsCocoaUtils::CocoaPointsToDevPixels(aPt, BackingScaleFactor());
   }
-  nsIntRect         CocoaPointsToDevPixels(const NSRect& aRect) const {
+  LayoutDeviceIntRect CocoaPointsToDevPixels(const NSRect& aRect) const {
     return nsCocoaUtils::CocoaPointsToDevPixels(aRect, BackingScaleFactor());
   }
   CGFloat           DevPixelsToCocoaPoints(int32_t aPixels) const {
     return nsCocoaUtils::DevPixelsToCocoaPoints(aPixels, BackingScaleFactor());
   }
-  NSRect            DevPixelsToCocoaPoints(const nsIntRect& aRect) const {
+  // XXX: all calls to this function should eventually be replaced with calls
+  // to DevPixelsToCocoaPoints().
+  NSRect            UntypedDevPixelsToCocoaPoints(const nsIntRect& aRect) const {
+    return nsCocoaUtils::UntypedDevPixelsToCocoaPoints(aRect, BackingScaleFactor());
+  }
+  NSRect            DevPixelsToCocoaPoints(const LayoutDeviceIntRect& aRect) const {
     return nsCocoaUtils::DevPixelsToCocoaPoints(aRect, BackingScaleFactor());
   }
 
@@ -577,19 +583,19 @@ protected:
   void ConfigureAPZCTreeManager() override;
   void ConfigureAPZControllerThread() override;
 
-  void DoRemoteComposition(const nsIntRect& aRenderRect);
+  void DoRemoteComposition(const LayoutDeviceIntRect& aRenderRect);
 
   // Overlay drawing functions for OpenGL drawing
-  void DrawWindowOverlay(mozilla::layers::GLManager* aManager, nsIntRect aRect);
-  void MaybeDrawResizeIndicator(mozilla::layers::GLManager* aManager, const nsIntRect& aRect);
-  void MaybeDrawRoundedCorners(mozilla::layers::GLManager* aManager, const nsIntRect& aRect);
-  void MaybeDrawTitlebar(mozilla::layers::GLManager* aManager, const nsIntRect& aRect);
+  void DrawWindowOverlay(mozilla::layers::GLManager* aManager, LayoutDeviceIntRect aRect);
+  void MaybeDrawResizeIndicator(mozilla::layers::GLManager* aManager);
+  void MaybeDrawRoundedCorners(mozilla::layers::GLManager* aManager, const LayoutDeviceIntRect& aRect);
+  void MaybeDrawTitlebar(mozilla::layers::GLManager* aManager);
 
   // Redraw the contents of mTitlebarCGContext on the main thread, as
   // determined by mDirtyTitlebarRegion.
   void UpdateTitlebarCGContext();
 
-  nsIntRect RectContainingTitlebarControls();
+  LayoutDeviceIntRect RectContainingTitlebarControls();
   void UpdateVibrancy(const nsTArray<ThemeGeometry>& aThemeGeometries);
   mozilla::VibrancyManager& EnsureVibrancyManager();
 
@@ -631,16 +637,16 @@ protected:
   // May be accessed from any thread, protected
   // by mEffectsLock.
   bool mShowsResizeIndicator;
-  nsIntRect mResizeIndicatorRect;
+  LayoutDeviceIntRect mResizeIndicatorRect;
   bool mHasRoundedBottomCorners;
   int mDevPixelCornerRadius;
   bool mIsCoveringTitlebar;
   bool mIsFullscreen;
-  nsIntRect mTitlebarRect;
+  LayoutDeviceIntRect mTitlebarRect;
 
   // The area of mTitlebarCGContext that needs to be redrawn during the next
   // transaction. Accessed from any thread, protected by mEffectsLock.
-  nsIntRegion mUpdatedTitlebarRegion;
+  LayoutDeviceIntRegion mUpdatedTitlebarRegion;
   CGContextRef mTitlebarCGContext;
 
   // Compositor thread only
@@ -653,7 +659,7 @@ protected:
   // uploaded to to mTitlebarImage. Main thread only.
   nsIntRegion           mDirtyTitlebarRegion;
 
-  nsIntRegion           mDraggableRegion;
+  LayoutDeviceIntRegion mDraggableRegion;
 
   // Cached value of [mView backingScaleFactor], to avoid sending two obj-c
   // messages (respondsToSelector, backingScaleFactor) every time we need to
diff --git a/widget/cocoa/nsChildView.mm b/widget/cocoa/nsChildView.mm
index 126f289e99bd..d7578af5cdaa 100644
--- a/widget/cocoa/nsChildView.mm
+++ b/widget/cocoa/nsChildView.mm
@@ -162,7 +162,7 @@ static uint32_t gNumberOfWidgetsNeedingEventThread = 0;
 - (void)processPendingRedraws;
 
 - (void)drawRect:(NSRect)aRect inContext:(CGContextRef)aContext;
-- (nsIntRegion)nativeDirtyRegionWithBoundingRect:(NSRect)aRect;
+- (LayoutDeviceIntRegion)nativeDirtyRegionWithBoundingRect:(NSRect)aRect;
 - (BOOL)isUsingMainThreadOpenGL;
 - (BOOL)isUsingOpenGL;
 - (void)drawUsingOpenGL;
@@ -279,13 +279,15 @@ public:
   virtual ~RectTextureImage();
 
   already_AddRefed<gfx::DrawTarget>
-    BeginUpdate(const nsIntSize& aNewSize,
-                const nsIntRegion& aDirtyRegion = nsIntRegion());
+    BeginUpdate(const LayoutDeviceIntSize& aNewSize,
+                const LayoutDeviceIntRegion& aDirtyRegion =
+                  LayoutDeviceIntRegion());
   void EndUpdate(bool aKeepSurface = false);
 
-  void UpdateIfNeeded(const nsIntSize& aNewSize,
-                      const nsIntRegion& aDirtyRegion,
-                      void (^aCallback)(gfx::DrawTarget*, const nsIntRegion&))
+  void UpdateIfNeeded(const LayoutDeviceIntSize& aNewSize,
+                      const LayoutDeviceIntRegion& aDirtyRegion,
+                      void (^aCallback)(gfx::DrawTarget*,
+                                        const LayoutDeviceIntRegion&))
   {
     RefPtr<gfx::DrawTarget> drawTarget = BeginUpdate(aNewSize, aDirtyRegion);
     if (drawTarget) {
@@ -294,29 +296,30 @@ public:
     }
   }
 
-  void UpdateFromCGContext(const nsIntSize& aNewSize,
-                           const nsIntRegion& aDirtyRegion,
+  void UpdateFromCGContext(const LayoutDeviceIntSize& aNewSize,
+                           const LayoutDeviceIntRegion& aDirtyRegion,
                            CGContextRef aCGContext);
 
-  nsIntRegion GetUpdateRegion() {
+  LayoutDeviceIntRegion GetUpdateRegion() {
     MOZ_ASSERT(mInUpdate, "update region only valid during update");
     return mUpdateRegion;
   }
 
   void Draw(mozilla::layers::GLManager* aManager,
-            const nsIntPoint& aLocation,
+            const LayoutDeviceIntPoint& aLocation,
             const Matrix4x4& aTransform = Matrix4x4());
 
-  static nsIntSize TextureSizeForSize(const nsIntSize& aSize);
+  static LayoutDeviceIntSize TextureSizeForSize(
+    const LayoutDeviceIntSize& aSize);
 
 protected:
 
   RefPtr<gfx::DrawTarget> mUpdateDrawTarget;
   GLContext* mGLContext;
-  nsIntRegion mUpdateRegion;
-  nsIntSize mUsedSize;
-  nsIntSize mBufferSize;
-  nsIntSize mTextureSize;
+  LayoutDeviceIntRegion mUpdateRegion;
+  LayoutDeviceIntSize mUsedSize;
+  LayoutDeviceIntSize mBufferSize;
+  LayoutDeviceIntSize mTextureSize;
   GLuint mTexture;
   bool mInUpdate;
 };
@@ -356,7 +359,7 @@ public:
                                const gfx::Rect& aLayerRect,
                                const gfx::Rect& aTextureRect) override;
 
-  void BeginFrame(nsIntSize aRenderSize);
+  void BeginFrame(LayoutDeviceIntSize aRenderSize);
   void EndFrame();
 
   NSOpenGLContext* GetNSOpenGLContext()
@@ -513,7 +516,8 @@ nsresult nsChildView::Create(nsIWidget *aParent,
   // create our parallel NSView and hook it up to our parent. Recall
   // that NS_NATIVE_WIDGET is the NSView.
   CGFloat scaleFactor = nsCocoaUtils::GetBackingScaleFactor(mParentView);
-  NSRect r = nsCocoaUtils::DevPixelsToCocoaPoints(mBounds, scaleFactor);
+  NSRect r = nsCocoaUtils::DevPixelsToCocoaPoints(
+    LayoutDeviceIntRect::FromUnknownRect(mBounds), scaleFactor);
   mView = [(NSView<mozView>*)CreateCocoaView(r) retain];
   if (!mView) {
     return NS_ERROR_FAILURE;
@@ -908,13 +912,9 @@ NS_IMETHODIMP nsChildView::SetCursor(imgIContainer* aCursor,
 // Get this component dimension
 NS_IMETHODIMP nsChildView::GetBounds(LayoutDeviceIntRect& aRect)
 {
-  nsIntRect tmp;
-  if (!mView) {
-    tmp = mBounds;
-  } else {
-    tmp = CocoaPointsToDevPixels([mView frame]);
-  }
-  aRect = LayoutDeviceIntRect::FromUnknownRect(tmp);
+  aRect = !mView
+        ? LayoutDeviceIntRect::FromUnknownRect(mBounds)
+        : CocoaPointsToDevPixels([mView frame]);
   return NS_OK;
 }
 
@@ -1006,7 +1006,7 @@ NS_IMETHODIMP nsChildView::Move(double aX, double aY)
   mBounds.y = y;
 
   ManipulateViewWithoutNeedingDisplay(mView, ^{
-    [mView setFrame:DevPixelsToCocoaPoints(mBounds)];
+    [mView setFrame:UntypedDevPixelsToCocoaPoints(mBounds)];
   });
 
   NotifyRollupGeometryChange();
@@ -1031,7 +1031,7 @@ NS_IMETHODIMP nsChildView::Resize(double aWidth, double aHeight, bool aRepaint)
   mBounds.height = height;
 
   ManipulateViewWithoutNeedingDisplay(mView, ^{
-    [mView setFrame:DevPixelsToCocoaPoints(mBounds)];
+    [mView setFrame:UntypedDevPixelsToCocoaPoints(mBounds)];
   });
 
   if (mVisible && aRepaint)
@@ -1070,7 +1070,7 @@ NS_IMETHODIMP nsChildView::Resize(double aX, double aY,
   }
 
   ManipulateViewWithoutNeedingDisplay(mView, ^{
-    [mView setFrame:DevPixelsToCocoaPoints(mBounds)];
+    [mView setFrame:UntypedDevPixelsToCocoaPoints(mBounds)];
   });
 
   if (mVisible && aRepaint)
@@ -1092,7 +1092,7 @@ NS_IMETHODIMP nsChildView::Resize(double aX, double aY,
 
 static const int32_t resizeIndicatorWidth = 15;
 static const int32_t resizeIndicatorHeight = 15;
-bool nsChildView::ShowsResizeIndicator(nsIntRect* aResizerRect)
+bool nsChildView::ShowsResizeIndicator(LayoutDeviceIntRect* aResizerRect)
 {
   NSView *topLevelView = mView, *superView = nil;
   while ((superView = [topLevelView superview]))
@@ -1364,10 +1364,10 @@ NS_IMETHODIMP nsChildView::Invalidate(const nsIntRect &aRect)
   if ([NSView focusView]) {
     // if a view is focussed (i.e. being drawn), then postpone the invalidate so that we
     // don't lose it.
-    [mView setNeedsPendingDisplayInRect:DevPixelsToCocoaPoints(aRect)];
+    [mView setNeedsPendingDisplayInRect:UntypedDevPixelsToCocoaPoints(aRect)];
   }
   else {
-    [mView setNeedsDisplayInRect:DevPixelsToCocoaPoints(aRect)];
+    [mView setNeedsDisplayInRect:UntypedDevPixelsToCocoaPoints(aRect)];
   }
 
   return NS_OK;
@@ -1941,7 +1941,7 @@ nsChildView::ConfigureAPZControllerThread()
   }
 }
 
-nsIntRect
+LayoutDeviceIntRect
 nsChildView::RectContainingTitlebarControls()
 {
   // Start with a thin strip at the top of the window for the highlight line.
@@ -2015,7 +2015,8 @@ nsChildView::PostRender(LayerManagerComposite* aManager)
 }
 
 void
-nsChildView::DrawWindowOverlay(LayerManagerComposite* aManager, nsIntRect aRect)
+nsChildView::DrawWindowOverlay(LayerManagerComposite* aManager,
+                               LayoutDeviceIntRect aRect)
 {
   nsAutoPtr<GLManager> manager(GLManager::CreateGLManager(aManager));
   if (manager) {
@@ -2024,20 +2025,20 @@ nsChildView::DrawWindowOverlay(LayerManagerComposite* aManager, nsIntRect aRect)
 }
 
 void
-nsChildView::DrawWindowOverlay(GLManager* aManager, nsIntRect aRect)
+nsChildView::DrawWindowOverlay(GLManager* aManager, LayoutDeviceIntRect aRect)
 {
   GLContext* gl = aManager->gl();
   ScopedGLState scopedScissorTestState(gl, LOCAL_GL_SCISSOR_TEST, false);
 
-  MaybeDrawTitlebar(aManager, aRect);
-  MaybeDrawResizeIndicator(aManager, aRect);
+  MaybeDrawTitlebar(aManager);
+  MaybeDrawResizeIndicator(aManager);
   MaybeDrawRoundedCorners(aManager, aRect);
 }
 
 static void
-ClearRegion(gfx::DrawTarget *aDT, nsIntRegion aRegion)
+ClearRegion(gfx::DrawTarget *aDT, LayoutDeviceIntRegion aRegion)
 {
-  gfxUtils::ClipToRegion(aDT, aRegion);
+  gfxUtils::ClipToRegion(aDT, aRegion.ToUnknownRegion());
   aDT->ClearRect(gfx::Rect(0, 0, aDT->GetSize().width, aDT->GetSize().height));
   aDT->PopClip();
 }
@@ -2076,7 +2077,7 @@ DrawResizer(CGContextRef aCtx)
 }
 
 void
-nsChildView::MaybeDrawResizeIndicator(GLManager* aManager, const nsIntRect& aRect)
+nsChildView::MaybeDrawResizeIndicator(GLManager* aManager)
 {
   MutexAutoLock lock(mEffectsLock);
   if (!mShowsResizeIndicator) {
@@ -2087,8 +2088,8 @@ nsChildView::MaybeDrawResizeIndicator(GLManager* aManager, const nsIntRect& aRec
     mResizerImage = new RectTextureImage(aManager->gl());
   }
 
-  nsIntSize size = mResizeIndicatorRect.Size();
-  mResizerImage->UpdateIfNeeded(size, nsIntRegion(), ^(gfx::DrawTarget* drawTarget, const nsIntRegion& updateRegion) {
+  LayoutDeviceIntSize size = mResizeIndicatorRect.Size();
+  mResizerImage->UpdateIfNeeded(size, LayoutDeviceIntRegion(), ^(gfx::DrawTarget* drawTarget, const LayoutDeviceIntRegion& updateRegion) {
     ClearRegion(drawTarget, updateRegion);
     gfx::BorrowedCGContext borrow(drawTarget);
     DrawResizer(borrow.cg);
@@ -2131,7 +2132,7 @@ DrawTitlebarHighlight(NSSize aWindowSize, CGFloat aRadius, CGFloat aDevicePixelW
 }
 
 static CGContextRef
-CreateCGContext(const nsIntSize& aSize)
+CreateCGContext(const LayoutDeviceIntSize& aSize)
 {
   CGColorSpaceRef cs = CGColorSpaceCreateDeviceRGB();
   CGContextRef ctx =
@@ -2164,7 +2165,8 @@ nsChildView::UpdateTitlebarCGContext()
   NSRect dirtyRect = [mView convertRect:[(BaseWindow*)[mView window] getAndResetNativeDirtyRect] fromView:nil];
   NSRect dirtyTitlebarRect = NSIntersectionRect(titlebarRect, dirtyRect);
 
-  nsIntSize texSize = RectTextureImage::TextureSizeForSize(mTitlebarRect.Size());
+  LayoutDeviceIntSize texSize =
+    RectTextureImage::TextureSizeForSize(mTitlebarRect.Size());
   if (!mTitlebarCGContext ||
       CGBitmapContextGetWidth(mTitlebarCGContext) != size_t(texSize.width) ||
       CGBitmapContextGetHeight(mTitlebarCGContext) != size_t(texSize.height)) {
@@ -2285,14 +2287,14 @@ nsChildView::UpdateTitlebarCGContext()
 // GLContext surface. In order to make the titlebar controls visible, we have
 // to redraw them inside the OpenGL context surface.
 void
-nsChildView::MaybeDrawTitlebar(GLManager* aManager, const nsIntRect& aRect)
+nsChildView::MaybeDrawTitlebar(GLManager* aManager)
 {
   MutexAutoLock lock(mEffectsLock);
   if (!mIsCoveringTitlebar || mIsFullscreen) {
     return;
   }
 
-  nsIntRegion updatedTitlebarRegion;
+  LayoutDeviceIntRegion updatedTitlebarRegion;
   updatedTitlebarRegion.And(mUpdatedTitlebarRegion, mTitlebarRect);
   mUpdatedTitlebarRegion.SetEmpty();
 
@@ -2315,7 +2317,8 @@ DrawTopLeftCornerMask(CGContextRef aCtx, int aRadius)
 }
 
 void
-nsChildView::MaybeDrawRoundedCorners(GLManager* aManager, const nsIntRect& aRect)
+nsChildView::MaybeDrawRoundedCorners(GLManager* aManager,
+                                     const LayoutDeviceIntRect& aRect)
 {
   MutexAutoLock lock(mEffectsLock);
 
@@ -2323,8 +2326,8 @@ nsChildView::MaybeDrawRoundedCorners(GLManager* aManager, const nsIntRect& aRect
     mCornerMaskImage = new RectTextureImage(aManager->gl());
   }
 
-  nsIntSize size(mDevPixelCornerRadius, mDevPixelCornerRadius);
-  mCornerMaskImage->UpdateIfNeeded(size, nsIntRegion(), ^(gfx::DrawTarget* drawTarget, const nsIntRegion& updateRegion) {
+  LayoutDeviceIntSize size(mDevPixelCornerRadius, mDevPixelCornerRadius);
+  mCornerMaskImage->UpdateIfNeeded(size, LayoutDeviceIntRegion(), ^(gfx::DrawTarget* drawTarget, const LayoutDeviceIntRegion& updateRegion) {
     ClearRegion(drawTarget, updateRegion);
     RefPtr<gfx::PathBuilder> builder = drawTarget->CreatePathBuilder();
     builder->Arc(gfx::Point(mDevPixelCornerRadius, mDevPixelCornerRadius), mDevPixelCornerRadius, 0, 2.0f * M_PI);
@@ -2392,17 +2395,17 @@ FindUnifiedToolbarBottom(const nsTArray<nsIWidget::ThemeGeometry>& aThemeGeometr
   return unifiedToolbarBottom;
 }
 
-static nsIntRect
+static LayoutDeviceIntRect
 FindFirstRectOfType(const nsTArray<nsIWidget::ThemeGeometry>& aThemeGeometries,
                     nsITheme::ThemeGeometryType aThemeGeometryType)
 {
   for (uint32_t i = 0; i < aThemeGeometries.Length(); ++i) {
     const nsIWidget::ThemeGeometry& g = aThemeGeometries[i];
     if (g.mType == aThemeGeometryType) {
-      return g.mRect;
+      return LayoutDeviceIntRect::FromUnknownRect(g.mRect);
     }
   }
-  return nsIntRect();
+  return LayoutDeviceIntRect();
 }
 
 void
@@ -2434,9 +2437,9 @@ nsChildView::UpdateThemeGeometries(const nsTArray<ThemeGeometry>& aThemeGeometri
   [win setSheetAttachmentPosition:DevPixelsToCocoaPoints(devSheetPosition)];
 
   // Update titlebar control offsets.
-  nsIntRect windowButtonRect = FindFirstRectOfType(aThemeGeometries, nsNativeThemeCocoa::eThemeGeometryTypeWindowButtons);
+  LayoutDeviceIntRect windowButtonRect = FindFirstRectOfType(aThemeGeometries, nsNativeThemeCocoa::eThemeGeometryTypeWindowButtons);
   [win placeWindowButtons:[mView convertRect:DevPixelsToCocoaPoints(windowButtonRect) toView:nil]];
-  nsIntRect fullScreenButtonRect = FindFirstRectOfType(aThemeGeometries, nsNativeThemeCocoa::eThemeGeometryTypeFullscreenButton);
+  LayoutDeviceIntRect fullScreenButtonRect = FindFirstRectOfType(aThemeGeometries, nsNativeThemeCocoa::eThemeGeometryTypeFullscreenButton);
   [win placeFullScreenButton:[mView convertRect:DevPixelsToCocoaPoints(fullScreenButtonRect) toView:nil]];
 }
 
@@ -2632,8 +2635,9 @@ nsChildView::StartRemoteDrawing()
     }
   }
 
-  nsIntRegion dirtyRegion = mBounds;
-  nsIntSize renderSize = mBounds.Size();
+  LayoutDeviceIntRegion dirtyRegion(LayoutDeviceIntRect::FromUnknownRect(mBounds));
+  LayoutDeviceIntSize renderSize =
+    LayoutDeviceIntSize::FromUnknownSize(mBounds.Size());
 
   if (!mBasicCompositorImage) {
     mBasicCompositorImage = new RectTextureImage(mGLPresenter->gl());
@@ -2644,7 +2648,7 @@ nsChildView::StartRemoteDrawing()
 
   if (!drawTarget) {
     // Composite unchanged textures.
-    DoRemoteComposition(mBounds);
+    DoRemoteComposition(LayoutDeviceIntRect::FromUnknownRect(mBounds));
     return nullptr;
   }
 
@@ -2655,7 +2659,7 @@ void
 nsChildView::EndRemoteDrawing()
 {
   mBasicCompositorImage->EndUpdate(true);
-  DoRemoteComposition(mBounds);
+  DoRemoteComposition(LayoutDeviceIntRect::FromUnknownRect(mBounds));
 }
 
 void
@@ -2682,7 +2686,7 @@ nsChildView::InitCompositor(Compositor* aCompositor)
 }
 
 void
-nsChildView::DoRemoteComposition(const nsIntRect& aRenderRect)
+nsChildView::DoRemoteComposition(const LayoutDeviceIntRect& aRenderRect)
 {
   if (![(ChildView*)mView preRender:mGLPresenter->GetNSOpenGLContext()]) {
     return;
@@ -2690,7 +2694,7 @@ nsChildView::DoRemoteComposition(const nsIntRect& aRenderRect)
   mGLPresenter->BeginFrame(aRenderRect.Size());
 
   // Draw the result from the basic compositor.
-  mBasicCompositorImage->Draw(mGLPresenter, nsIntPoint(0, 0));
+  mBasicCompositorImage->Draw(mGLPresenter, LayoutDeviceIntPoint(0, 0));
 
   // DrawWindowOverlay doesn't do anything for non-GL, so it didn't paint
   // anything during the basic compositor transaction. Draw the overlay now.
@@ -2704,8 +2708,10 @@ nsChildView::DoRemoteComposition(const nsIntRect& aRenderRect)
 void
 nsChildView::UpdateWindowDraggingRegion(const nsIntRegion& aRegion)
 {
-  if (mDraggableRegion != aRegion) {
-    mDraggableRegion = aRegion;
+  LayoutDeviceIntRegion region =
+    LayoutDeviceIntRegion::FromUnknownRegion(aRegion);
+  if (mDraggableRegion != region) {
+    mDraggableRegion = region;
     [(ChildView*)mView updateWindowDraggableState];
   }
 }
@@ -2875,29 +2881,30 @@ RectTextureImage::~RectTextureImage()
   }
 }
 
-nsIntSize
-RectTextureImage::TextureSizeForSize(const nsIntSize& aSize)
+LayoutDeviceIntSize
+RectTextureImage::TextureSizeForSize(const LayoutDeviceIntSize& aSize)
 {
-  return nsIntSize(gfx::NextPowerOfTwo(aSize.width),
-                   gfx::NextPowerOfTwo(aSize.height));
+  return LayoutDeviceIntSize(gfx::NextPowerOfTwo(aSize.width),
+                             gfx::NextPowerOfTwo(aSize.height));
 }
 
 already_AddRefed<gfx::DrawTarget>
-RectTextureImage::BeginUpdate(const nsIntSize& aNewSize,
-                              const nsIntRegion& aDirtyRegion)
+RectTextureImage::BeginUpdate(const LayoutDeviceIntSize& aNewSize,
+                              const LayoutDeviceIntRegion& aDirtyRegion)
 {
   MOZ_ASSERT(!mInUpdate, "Beginning update during update!");
   mUpdateRegion = aDirtyRegion;
   if (aNewSize != mUsedSize) {
     mUsedSize = aNewSize;
-    mUpdateRegion = gfx::IntRect(gfx::IntPoint(0, 0), aNewSize);
+    mUpdateRegion =
+      LayoutDeviceIntRect(LayoutDeviceIntPoint(0, 0), aNewSize);
   }
 
   if (mUpdateRegion.IsEmpty()) {
     return nullptr;
   }
 
-  nsIntSize neededBufferSize = TextureSizeForSize(mUsedSize);
+  LayoutDeviceIntSize neededBufferSize = TextureSizeForSize(mUsedSize);
   if (!mUpdateDrawTarget || mBufferSize != neededBufferSize) {
     gfx::IntSize size(neededBufferSize.width, neededBufferSize.height);
     mUpdateDrawTarget =
@@ -2926,14 +2933,15 @@ RectTextureImage::EndUpdate(bool aKeepSurface)
   MOZ_ASSERT(mInUpdate, "Ending update while not in update");
 
   bool overwriteTexture = false;
-  nsIntRegion updateRegion = mUpdateRegion;
+  LayoutDeviceIntRegion updateRegion = mUpdateRegion;
   if (!mTexture || (mTextureSize != mBufferSize)) {
     overwriteTexture = true;
     mTextureSize = mBufferSize;
   }
 
   if (overwriteTexture || !CanUploadSubtextures()) {
-    updateRegion = gfx::IntRect(gfx::IntPoint(0, 0), mTextureSize);
+    updateRegion =
+      LayoutDeviceIntRect(LayoutDeviceIntPoint(0, 0), mTextureSize);
   }
 
   RefPtr<gfx::SourceSurface> snapshot = mUpdateDrawTarget->Snapshot();
@@ -2941,10 +2949,10 @@ RectTextureImage::EndUpdate(bool aKeepSurface)
 
   UploadSurfaceToTexture(mGLContext,
                          dataSnapshot,
-                         updateRegion,
+                         updateRegion.ToUnknownRegion(),
                          mTexture,
                          overwriteTexture,
-                         updateRegion.GetBounds().TopLeft(),
+                         updateRegion.GetBounds().TopLeft().ToUnknownPoint(),
                          false,
                          LOCAL_GL_TEXTURE0,
                          LOCAL_GL_TEXTURE_RECTANGLE_ARB);
@@ -2957,8 +2965,8 @@ RectTextureImage::EndUpdate(bool aKeepSurface)
 }
 
 void
-RectTextureImage::UpdateFromCGContext(const nsIntSize& aNewSize,
-                                      const nsIntRegion& aDirtyRegion,
+RectTextureImage::UpdateFromCGContext(const LayoutDeviceIntSize& aNewSize,
+                                      const LayoutDeviceIntRegion& aDirtyRegion,
                                       CGContextRef aCGContext)
 {
   gfx::IntSize size = gfx::IntSize(CGBitmapContextGetWidth(aCGContext),
@@ -2967,7 +2975,7 @@ RectTextureImage::UpdateFromCGContext(const nsIntSize& aNewSize,
   RefPtr<gfx::DrawTarget> dt = BeginUpdate(aNewSize, aDirtyRegion);
   if (dt) {
     gfx::Rect rect(0, 0, size.width, size.height);
-    gfxUtils::ClipToRegion(dt, GetUpdateRegion());
+    gfxUtils::ClipToRegion(dt, GetUpdateRegion().ToUnknownRegion());
     RefPtr<gfx::SourceSurface> sourceSurface =
       dt->CreateSourceSurfaceFromData(static_cast<uint8_t *>(CGBitmapContextGetData(aCGContext)),
                                       size,
@@ -2983,7 +2991,7 @@ RectTextureImage::UpdateFromCGContext(const nsIntSize& aNewSize,
 
 void
 RectTextureImage::Draw(GLManager* aManager,
-                       const nsIntPoint& aLocation,
+                       const LayoutDeviceIntPoint& aLocation,
                        const Matrix4x4& aTransform)
 {
   ShaderProgramOGL* program = aManager->GetProgram(LOCAL_GL_TEXTURE_RECTANGLE_ARB,
@@ -3076,7 +3084,7 @@ GLPresenter::BindAndDrawQuad(ShaderProgramOGL *aProgram,
 }
 
 void
-GLPresenter::BeginFrame(nsIntSize aRenderSize)
+GLPresenter::BeginFrame(LayoutDeviceIntSize aRenderSize)
 {
   mGLContext->MakeCurrent();
 
@@ -3610,9 +3618,9 @@ NSEvent* gLastDragMouseDownEvent = nil;
   return mGeckoChild->VibrancyFontSmoothingBackgroundColorForThemeGeometryType(aThemeGeometryType);
 }
 
-- (nsIntRegion)nativeDirtyRegionWithBoundingRect:(NSRect)aRect
+- (LayoutDeviceIntRegion)nativeDirtyRegionWithBoundingRect:(NSRect)aRect
 {
-  nsIntRect boundingRect = mGeckoChild->CocoaPointsToDevPixels(aRect);
+  LayoutDeviceIntRect boundingRect = mGeckoChild->CocoaPointsToDevPixels(aRect);
   const NSRect *rects;
   NSInteger count;
   [self getRectsBeingDrawn:&rects count:&count];
@@ -3621,7 +3629,7 @@ NSEvent* gLastDragMouseDownEvent = nil;
     return boundingRect;
   }
 
-  nsIntRegion region;
+  LayoutDeviceIntRegion region;
   for (NSInteger i = 0; i < count; ++i) {
     region.Or(region, mGeckoChild->CocoaPointsToDevPixels(rects[i]));
   }
@@ -3698,7 +3706,7 @@ NSEvent* gLastDragMouseDownEvent = nil;
 
   CGContextSaveGState(aContext);
 
-  nsIntRegion region = [self nativeDirtyRegionWithBoundingRect:aRect];
+  LayoutDeviceIntRegion region = [self nativeDirtyRegionWithBoundingRect:aRect];
 
   // Create Cairo objects.
   RefPtr<gfxQuartzSurface> targetSurface;
@@ -3712,10 +3720,10 @@ NSEvent* gLastDragMouseDownEvent = nil;
   RefPtr<gfxContext> targetContext = new gfxContext(dt);
 
   // Set up the clip region.
-  nsIntRegionRectIterator iter(region);
+  LayoutDeviceIntRegion::RectIterator iter(region);
   targetContext->NewPath();
   for (;;) {
-    const nsIntRect* r = iter.Next();
+    const LayoutDeviceIntRect* r = iter.Next();
     if (!r)
       break;
     targetContext->Rectangle(gfxRect(r->x, r->y, r->width, r->height));
@@ -3727,10 +3735,10 @@ NSEvent* gLastDragMouseDownEvent = nil;
   if (mGeckoChild->GetLayerManager()->GetBackendType() == LayersBackend::LAYERS_BASIC) {
     nsBaseWidget::AutoLayerManagerSetup
       setupLayerManager(mGeckoChild, targetContext, BufferMode::BUFFER_NONE);
-    painted = mGeckoChild->PaintWindow(region);
+    painted = mGeckoChild->PaintWindow(region.ToUnknownRegion());
   } else if (mGeckoChild->GetLayerManager()->GetBackendType() == LayersBackend::LAYERS_CLIENT) {
     // We only need this so that we actually get DidPaintWindow fired
-    painted = mGeckoChild->PaintWindow(region);
+    painted = mGeckoChild->PaintWindow(region.ToUnknownRegion());
   }
 
   targetContext = nullptr;
@@ -4588,15 +4596,16 @@ NSEvent* gLastDragMouseDownEvent = nil;
 }
 
 static CGSRegionObj
-NewCGSRegionFromRegion(const nsIntRegion& aRegion,
-                       CGRect (^aRectConverter)(const nsIntRect&))
+NewCGSRegionFromRegion(const LayoutDeviceIntRegion& aRegion,
+                       CGRect (^aRectConverter)(const LayoutDeviceIntRect&))
 {
   nsTArray<CGRect> rects;
-  nsIntRegionRectIterator iter(aRegion);
+  LayoutDeviceIntRegion::RectIterator iter(aRegion);
   for (;;) {
-    const nsIntRect* r = iter.Next();
-    if (!r)
+    const LayoutDeviceIntRect* r = iter.Next();
+    if (!r) {
       break;
+    }
     rects.AppendElement(aRectConverter(*r));
   }
 
@@ -4615,12 +4624,12 @@ NewCGSRegionFromRegion(const nsIntRegion& aRegion,
     return [super _regionForOpaqueDescendants:aRect forMove:aForMove];
   }
 
-  nsIntRect boundingRect = mGeckoChild->CocoaPointsToDevPixels(aRect);
+  LayoutDeviceIntRect boundingRect = mGeckoChild->CocoaPointsToDevPixels(aRect);
 
-  nsIntRegion opaqueRegion;
+  LayoutDeviceIntRegion opaqueRegion;
   opaqueRegion.Sub(boundingRect, mGeckoChild->GetDraggableRegion());
 
-  return NewCGSRegionFromRegion(opaqueRegion, ^(const nsIntRect& r) {
+  return NewCGSRegionFromRegion(opaqueRegion, ^(const LayoutDeviceIntRect& r) {
     return [self convertToFlippedWindowCoordinates:mGeckoChild->DevPixelsToCocoaPoints(r)];
   });
 }
diff --git a/widget/cocoa/nsCocoaUtils.h b/widget/cocoa/nsCocoaUtils.h
index e5a13120ab98..287cec0b4480 100644
--- a/widget/cocoa/nsCocoaUtils.h
+++ b/widget/cocoa/nsCocoaUtils.h
@@ -129,6 +129,7 @@ struct KeyBindingsCommand
 class nsCocoaUtils
 {
   typedef mozilla::gfx::SourceSurface SourceSurface;
+  typedef mozilla::LayoutDeviceIntRect LayoutDeviceIntRect;
 
 public:
 
@@ -159,13 +160,13 @@ public:
                       NSToIntRound(aPt.y * aBackingScale));
   }
 
-  static nsIntRect
+  static LayoutDeviceIntRect
   CocoaPointsToDevPixels(const NSRect& aRect, CGFloat aBackingScale)
   {
-    return nsIntRect(NSToIntRound(aRect.origin.x * aBackingScale),
-                     NSToIntRound(aRect.origin.y * aBackingScale),
-                     NSToIntRound(aRect.size.width * aBackingScale),
-                     NSToIntRound(aRect.size.height * aBackingScale));
+    return LayoutDeviceIntRect(NSToIntRound(aRect.origin.x * aBackingScale),
+                               NSToIntRound(aRect.origin.y * aBackingScale),
+                               NSToIntRound(aRect.size.width * aBackingScale),
+                               NSToIntRound(aRect.size.height * aBackingScale));
   }
 
   static CGFloat
@@ -182,8 +183,20 @@ public:
                        (CGFloat)aPt.y / aBackingScale);
   }
 
+  // XXX: all calls to this function should eventually be replaced with calls
+  // to DevPixelsToCocoaPoints().
   static NSRect
-  DevPixelsToCocoaPoints(const nsIntRect& aRect, CGFloat aBackingScale)
+  UntypedDevPixelsToCocoaPoints(const nsIntRect& aRect, CGFloat aBackingScale)
+  {
+    return NSMakeRect((CGFloat)aRect.x / aBackingScale,
+                      (CGFloat)aRect.y / aBackingScale,
+                      (CGFloat)aRect.width / aBackingScale,
+                      (CGFloat)aRect.height / aBackingScale);
+  }
+
+  static NSRect
+  DevPixelsToCocoaPoints(const LayoutDeviceIntRect& aRect,
+                         CGFloat aBackingScale)
   {
     return NSMakeRect((CGFloat)aRect.x / aBackingScale,
                       (CGFloat)aRect.y / aBackingScale,
@@ -217,8 +230,8 @@ public:
   // See explanation for geckoRectToCocoaRect, guess what this does...
   static nsIntRect CocoaRectToGeckoRect(const NSRect &cocoaRect);
 
-  static nsIntRect CocoaRectToGeckoRectDevPix(const NSRect &aCocoaRect,
-                                              CGFloat aBackingScale);
+  static mozilla::LayoutDeviceIntRect CocoaRectToGeckoRectDevPix(
+    const NSRect& aCocoaRect, CGFloat aBackingScale);
 
   // Gives the location for the event in screen coordinates. Do not call this
   // unless the window the event was originally targeted at is still alive!
diff --git a/widget/cocoa/nsCocoaUtils.mm b/widget/cocoa/nsCocoaUtils.mm
index 8a3adb2cc840..fa475a1d8563 100644
--- a/widget/cocoa/nsCocoaUtils.mm
+++ b/widget/cocoa/nsCocoaUtils.mm
@@ -97,10 +97,10 @@ nsIntRect nsCocoaUtils::CocoaRectToGeckoRect(const NSRect &cocoaRect)
   return rect;
 }
 
-nsIntRect nsCocoaUtils::CocoaRectToGeckoRectDevPix(const NSRect &aCocoaRect,
-                                                   CGFloat aBackingScale)
+LayoutDeviceIntRect nsCocoaUtils::CocoaRectToGeckoRectDevPix(
+  const NSRect& aCocoaRect, CGFloat aBackingScale)
 {
-  nsIntRect rect;
+  LayoutDeviceIntRect rect;
   rect.x = NSToIntRound(aCocoaRect.origin.x * aBackingScale);
   rect.y = NSToIntRound(FlippedScreenY(aCocoaRect.origin.y + aCocoaRect.size.height) * aBackingScale);
   rect.width = NSToIntRound((aCocoaRect.origin.x + aCocoaRect.size.width) * aBackingScale) - rect.x;
diff --git a/widget/cocoa/nsCocoaWindow.mm b/widget/cocoa/nsCocoaWindow.mm
index 5adf27fd87dd..7964805a2197 100644
--- a/widget/cocoa/nsCocoaWindow.mm
+++ b/widget/cocoa/nsCocoaWindow.mm
@@ -1573,8 +1573,7 @@ NS_IMETHODIMP nsCocoaWindow::GetClientBounds(mozilla::LayoutDeviceIntRect& aRect
 
   CGFloat scaleFactor = BackingScaleFactor();
   if (!mWindow) {
-    aRect = LayoutDeviceIntRect::FromUnknownRect(
-      nsCocoaUtils::CocoaRectToGeckoRectDevPix(NSZeroRect, scaleFactor));
+    aRect = nsCocoaUtils::CocoaRectToGeckoRectDevPix(NSZeroRect, scaleFactor);
     return NS_OK;
   }
 
@@ -1586,8 +1585,7 @@ NS_IMETHODIMP nsCocoaWindow::GetClientBounds(mozilla::LayoutDeviceIntRect& aRect
     r = [mWindow contentRectForFrameRect:[mWindow frame]];
   }
 
-  aRect = LayoutDeviceIntRect::FromUnknownRect(
-    nsCocoaUtils::CocoaRectToGeckoRectDevPix(r, scaleFactor));
+  aRect = nsCocoaUtils::CocoaRectToGeckoRectDevPix(r, scaleFactor);
 
   return NS_OK;
 
@@ -1601,7 +1599,8 @@ nsCocoaWindow::UpdateBounds()
   if (mWindow) {
     frame = [mWindow frame];
   }
-  mBounds = nsCocoaUtils::CocoaRectToGeckoRectDevPix(frame, BackingScaleFactor());
+  mBounds = nsCocoaUtils::CocoaRectToGeckoRectDevPix(
+    frame, BackingScaleFactor()).ToUnknownRect();
 }
 
 NS_IMETHODIMP nsCocoaWindow::GetScreenBounds(LayoutDeviceIntRect &aRect)
@@ -1609,8 +1608,8 @@ NS_IMETHODIMP nsCocoaWindow::GetScreenBounds(LayoutDeviceIntRect &aRect)
   NS_OBJC_BEGIN_TRY_ABORT_BLOCK_NSRESULT;
 
 #ifdef DEBUG
-  nsIntRect r = nsCocoaUtils::CocoaRectToGeckoRectDevPix([mWindow frame], BackingScaleFactor());
-  NS_ASSERTION(mWindow && mBounds == r, "mBounds out of sync!");
+  LayoutDeviceIntRect r = nsCocoaUtils::CocoaRectToGeckoRectDevPix([mWindow frame], BackingScaleFactor());
+  NS_ASSERTION(mWindow && mBounds == r.ToUnknownRect(), "mBounds out of sync!");
 #endif
 
   aRect = LayoutDeviceIntRect::FromUnknownRect(mBounds);
@@ -1986,13 +1985,13 @@ LayoutDeviceIntPoint nsCocoaWindow::WidgetToScreenOffset()
   NS_OBJC_BEGIN_TRY_ABORT_BLOCK_RETURN;
 
   NSRect rect = NSZeroRect;
-  nsIntRect r;
+  LayoutDeviceIntRect r;
   if (mWindow) {
     rect = [mWindow contentRectForFrameRect:[mWindow frame]];
   }
   r = nsCocoaUtils::CocoaRectToGeckoRectDevPix(rect, BackingScaleFactor());
 
-  return LayoutDeviceIntPoint::FromUnknownPoint(r.TopLeft());
+  return r.TopLeft();
 
   NS_OBJC_END_TRY_ABORT_BLOCK_RETURN(LayoutDeviceIntPoint(0,0));
 }
@@ -2019,12 +2018,12 @@ nsCocoaWindow::ClientToWindowSize(const LayoutDeviceIntSize& aClientSize)
     return LayoutDeviceIntSize(0, 0);
 
   CGFloat backingScale = BackingScaleFactor();
-  nsIntRect r(0, 0, aClientSize.width, aClientSize.height);
+  LayoutDeviceIntRect r(0, 0, aClientSize.width, aClientSize.height);
   NSRect rect = nsCocoaUtils::DevPixelsToCocoaPoints(r, backingScale);
 
   NSRect inflatedRect = [mWindow frameRectForContentRect:rect];
   r = nsCocoaUtils::CocoaRectToGeckoRectDevPix(inflatedRect, backingScale);
-  return LayoutDeviceIntSize(r.width, r.height);
+  return r.Size();
 
   NS_OBJC_END_TRY_ABORT_BLOCK_RETURN(LayoutDeviceIntSize(0,0));
 }
diff --git a/widget/cocoa/nsScreenCocoa.mm b/widget/cocoa/nsScreenCocoa.mm
index 5a9ccb6e26cb..1b72bbf82e16 100644
--- a/widget/cocoa/nsScreenCocoa.mm
+++ b/widget/cocoa/nsScreenCocoa.mm
@@ -44,7 +44,8 @@ nsScreenCocoa::GetRect(int32_t *outX, int32_t *outY, int32_t *outWidth, int32_t
 {
   NSRect frame = [mScreen frame];
 
-  nsIntRect r = nsCocoaUtils::CocoaRectToGeckoRectDevPix(frame, BackingScaleFactor());
+  LayoutDeviceIntRect r =
+    nsCocoaUtils::CocoaRectToGeckoRectDevPix(frame, BackingScaleFactor());
 
   *outX = r.x;
   *outY = r.y;
@@ -59,7 +60,8 @@ nsScreenCocoa::GetAvailRect(int32_t *outX, int32_t *outY, int32_t *outWidth, int
 {
   NSRect frame = [mScreen visibleFrame];
 
-  nsIntRect r = nsCocoaUtils::CocoaRectToGeckoRectDevPix(frame, BackingScaleFactor());
+  LayoutDeviceIntRect r =
+    nsCocoaUtils::CocoaRectToGeckoRectDevPix(frame, BackingScaleFactor());
 
   *outX = r.x;
   *outY = r.y;
diff --git a/widget/nsBaseWidget.cpp b/widget/nsBaseWidget.cpp
index 1eb406e6ff6c..31b40108403c 100644
--- a/widget/nsBaseWidget.cpp
+++ b/widget/nsBaseWidget.cpp
@@ -1479,7 +1479,7 @@ nsBaseWidget::SetWindowTitlebarColor(nscolor aColor, bool aActive)
 }
 
 bool
-nsBaseWidget::ShowsResizeIndicator(nsIntRect* aResizerRect)
+nsBaseWidget::ShowsResizeIndicator(LayoutDeviceIntRect* aResizerRect)
 {
   return false;
 }
diff --git a/widget/nsBaseWidget.h b/widget/nsBaseWidget.h
index bc179660f301..51673e3382f3 100644
--- a/widget/nsBaseWidget.h
+++ b/widget/nsBaseWidget.h
@@ -167,7 +167,7 @@ public:
   virtual bool            PreRender(LayerManagerComposite* aManager) override { return true; }
   virtual void            PostRender(LayerManagerComposite* aManager) override {}
   virtual void            DrawWindowUnderlay(LayerManagerComposite* aManager, nsIntRect aRect) override {}
-  virtual void            DrawWindowOverlay(LayerManagerComposite* aManager, nsIntRect aRect) override {}
+  virtual void            DrawWindowOverlay(LayerManagerComposite* aManager, LayoutDeviceIntRect aRect) override {}
   virtual already_AddRefed<mozilla::gfx::DrawTarget> StartRemoteDrawing() override;
   virtual void            EndRemoteDrawing() override { };
   virtual void            CleanupRemoteDrawing() override { };
@@ -202,7 +202,7 @@ public:
   NS_IMETHOD              SetIcon(const nsAString &anIconSpec) override;
   NS_IMETHOD              SetWindowTitlebarColor(nscolor aColor, bool aActive) override;
   virtual void            SetDrawsInTitlebar(bool aState) override {}
-  virtual bool            ShowsResizeIndicator(nsIntRect* aResizerRect) override;
+  virtual bool            ShowsResizeIndicator(LayoutDeviceIntRect* aResizerRect) override;
   virtual void            FreeNativeData(void * data, uint32_t aDataType) override {}
   NS_IMETHOD              BeginResizeDrag(mozilla::WidgetGUIEvent* aEvent,
                                           int32_t aHorizontal,
diff --git a/widget/nsIWidget.h b/widget/nsIWidget.h
index 0584e6c96ad8..0c3b36c72f8f 100644
--- a/widget/nsIWidget.h
+++ b/widget/nsIWidget.h
@@ -335,6 +335,7 @@ class nsIWidget : public nsISupports {
     typedef mozilla::LayoutDeviceIntMargin LayoutDeviceIntMargin;
     typedef mozilla::LayoutDeviceIntPoint LayoutDeviceIntPoint;
     typedef mozilla::LayoutDeviceIntRect LayoutDeviceIntRect;
+    typedef mozilla::LayoutDeviceIntRegion LayoutDeviceIntRegion;
     typedef mozilla::LayoutDeviceIntSize LayoutDeviceIntSize;
 
     // Used in UpdateThemeGeometries.
@@ -1258,7 +1259,8 @@ class nsIWidget : public nsISupports {
      *
      * Always called from the compositing thread.
      */
-    virtual void DrawWindowOverlay(LayerManagerComposite* aManager, nsIntRect aRect) = 0;
+    virtual void DrawWindowOverlay(LayerManagerComposite* aManager,
+                                   LayoutDeviceIntRect aRect) = 0;
 
     /**
      * Return a DrawTarget for the window which can be composited into.
@@ -1500,7 +1502,7 @@ class nsIWidget : public nsISupports {
      * @param aResizerRect The resizer's rect in device pixels.
      * @return Whether a resize widget is shown.
      */
-    virtual bool ShowsResizeIndicator(nsIntRect* aResizerRect) = 0;
+    virtual bool ShowsResizeIndicator(LayoutDeviceIntRect* aResizerRect) = 0;
 
     /**
      * Return the popup that was last rolled up, or null if there isn't one.