diff --git a/docshell/base/nsDocShell.cpp b/docshell/base/nsDocShell.cpp
index c809874b258b..8c2522400036 100644
--- a/docshell/base/nsDocShell.cpp
+++ b/docshell/base/nsDocShell.cpp
@@ -6884,9 +6884,9 @@ nsresult nsDocShell::CaptureState() {
 
   // Capture the current content viewer bounds.
   if (mDocumentViewer) {
-    nsIntRect bounds;
+    LayoutDeviceIntRect bounds;
     mDocumentViewer->GetBounds(bounds);
-    mOSHE->SetViewerBounds(bounds);
+    mOSHE->SetViewerBounds(bounds.ToUnknownRect());
   }
 
   // Capture the docshell hierarchy.
@@ -7234,7 +7234,7 @@ nsresult nsDocShell::RestoreFromHistory() {
 
   nsView* rootViewSibling = nullptr;
   nsView* rootViewParent = nullptr;
-  nsIntRect newBounds(0, 0, 0, 0);
+  LayoutDeviceIntRect newBounds(0, 0, 0, 0);
 
   PresShell* oldPresShell = GetPresShell();
   if (oldPresShell) {
@@ -7541,7 +7541,8 @@ nsresult nsDocShell::RestoreFromHistory() {
   // cached viewer size (skipping the resize if they are equal).
 
   if (newRootView) {
-    if (!newBounds.IsEmpty() && !newBounds.IsEqualEdges(oldBounds)) {
+    if (!newBounds.IsEmpty() &&
+        !newBounds.ToUnknownRect().IsEqualEdges(oldBounds)) {
       MOZ_LOG(gPageCacheLog, LogLevel::Debug,
               ("resize widget(%d, %d, %d, %d)", newBounds.x, newBounds.y,
                newBounds.width, newBounds.height));
@@ -7938,7 +7939,7 @@ nsresult nsDocShell::SetupNewViewer(nsIDocumentViewer* aNewViewer,
   nsCOMPtr<nsIWidget> widget;
   NS_ENSURE_SUCCESS(GetMainWidget(getter_AddRefs(widget)), NS_ERROR_FAILURE);
 
-  nsIntRect bounds(x, y, cx, cy);
+  LayoutDeviceIntRect bounds(x, y, cx, cy);
 
   mDocumentViewer->SetNavigationTiming(mTiming);
 
diff --git a/docshell/base/nsDocShell.h b/docshell/base/nsDocShell.h
index 0cf72f8fffb4..26772871c39d 100644
--- a/docshell/base/nsDocShell.h
+++ b/docshell/base/nsDocShell.h
@@ -1163,7 +1163,7 @@ class nsDocShell final : public nsDocLoader,
   nsWeakPtr mBrowserChild;
 
   // Dimensions of the docshell
-  nsIntRect mBounds;
+  mozilla::LayoutDeviceIntRect mBounds;
 
   /**
    * Content-Type Hint of the most-recently initiated load. Used for
diff --git a/docshell/base/nsIDocumentViewer.idl b/docshell/base/nsIDocumentViewer.idl
index 27510dc87905..ec6c864c18b1 100644
--- a/docshell/base/nsIDocumentViewer.idl
+++ b/docshell/base/nsIDocumentViewer.idl
@@ -33,7 +33,7 @@ class RemotePrintJobChild;
 %}
 
 [ptr] native nsIWidgetPtr(nsIWidget);
-[ref] native nsIntRectRef(nsIntRect);
+[ref] native LayoutDeviceIntRectRef(mozilla::LayoutDeviceIntRect);
 [ptr] native nsPresContextPtr(nsPresContext);
 [ptr] native nsViewPtr(nsView);
 [ptr] native nsDOMNavigationTimingPtr(nsDOMNavigationTiming);
@@ -46,7 +46,7 @@ class RemotePrintJobChild;
 interface nsIDocumentViewer : nsISupports
 {
   [noscript] void init(in nsIWidgetPtr aParentWidget,
-                       [const] in nsIntRectRef aBounds,
+                       [const] in LayoutDeviceIntRectRef aBounds,
                        in WindowGlobalChildPtr aWindowActor);
 
   attribute nsIDocShell container;
@@ -163,13 +163,13 @@ interface nsIDocumentViewer : nsISupports
    */
   [noscript,nostdcall] void setDocument(in Document aDocument);
 
-  [noscript] void getBounds(in nsIntRectRef aBounds);
-  [noscript] void setBounds([const] in nsIntRectRef aBounds);
+  [noscript] void getBounds(in LayoutDeviceIntRectRef aBounds);
+  [noscript] void setBounds([const] in LayoutDeviceIntRectRef aBounds);
   /**
    * The 'aFlags' argument to setBoundsWithFlags is a set of these bits.
    */
   const unsigned long eDelayResize = 1;
-  [noscript] void setBoundsWithFlags([const] in nsIntRectRef aBounds,
+  [noscript] void setBoundsWithFlags([const] in LayoutDeviceIntRectRef aBounds,
                                      in unsigned long aFlags);
 
   /**
diff --git a/dom/base/Document.cpp b/dom/base/Document.cpp
index f9daaecc3591..c233c00f8608 100644
--- a/dom/base/Document.cpp
+++ b/dom/base/Document.cpp
@@ -993,7 +993,7 @@ nsresult ExternalResourceMap::AddExternalResource(nsIURI* aURI,
     // Make sure that hiding our viewer will tear down its presentation.
     aViewer->SetSticky(false);
 
-    rv = aViewer->Init(nullptr, nsIntRect(0, 0, 0, 0), nullptr);
+    rv = aViewer->Init(nullptr, LayoutDeviceIntRect(), nullptr);
     if (NS_SUCCEEDED(rv)) {
       rv = aViewer->Open(nullptr, nullptr);
     }
diff --git a/dom/base/nsDOMWindowUtils.cpp b/dom/base/nsDOMWindowUtils.cpp
index 848b7d717711..6266290dd9f6 100644
--- a/dom/base/nsDOMWindowUtils.cpp
+++ b/dom/base/nsDOMWindowUtils.cpp
@@ -3654,17 +3654,14 @@ static void PrepareForFullscreenChange(nsIDocShell* aDocShell,
     nsCOMPtr<nsIDocumentViewer> viewer;
     aDocShell->GetDocViewer(getter_AddRefs(viewer));
     if (viewer) {
-      nsIntRect viewerBounds;
+      LayoutDeviceIntRect viewerBounds;
       viewer->GetBounds(viewerBounds);
       nscoord auPerDev = presShell->GetPresContext()->AppUnitsPerDevPixel();
       if (aOldSize) {
-        *aOldSize = LayoutDeviceIntSize::ToAppUnits(
-            LayoutDeviceIntSize::FromUnknownSize(viewerBounds.Size()),
-            auPerDev);
+        *aOldSize =
+            LayoutDeviceIntSize::ToAppUnits(viewerBounds.Size(), auPerDev);
       }
-      LayoutDeviceIntSize newSize =
-          LayoutDeviceIntSize::FromAppUnitsRounded(aSize, auPerDev);
-
+      auto newSize = LayoutDeviceIntSize::FromAppUnitsRounded(aSize, auPerDev);
       viewerBounds.SizeTo(newSize.width, newSize.height);
       viewer->SetBounds(viewerBounds);
     }
diff --git a/gfx/thebes/gfxSVGGlyphs.cpp b/gfx/thebes/gfxSVGGlyphs.cpp
index 4afeace2c409..a668f9070337 100644
--- a/gfx/thebes/gfxSVGGlyphs.cpp
+++ b/gfx/thebes/gfxSVGGlyphs.cpp
@@ -138,7 +138,7 @@ nsresult gfxSVGGlyphsDocument::SetupPresentation() {
   NS_ENSURE_SUCCESS(rv, rv);
 
   auto upem = mOwner->FontEntry()->UnitsPerEm();
-  rv = viewer->Init(nullptr, gfx::IntRect(0, 0, upem, upem), nullptr);
+  rv = viewer->Init(nullptr, LayoutDeviceIntRect(0, 0, upem, upem), nullptr);
   if (NS_SUCCEEDED(rv)) {
     rv = viewer->Open(nullptr, nullptr);
     NS_ENSURE_SUCCESS(rv, rv);
diff --git a/image/SVGDocumentWrapper.cpp b/image/SVGDocumentWrapper.cpp
index bf29d8d64dd7..b2f9f6c26b98 100644
--- a/image/SVGDocumentWrapper.cpp
+++ b/image/SVGDocumentWrapper.cpp
@@ -72,12 +72,14 @@ void SVGDocumentWrapper::UpdateViewportBounds(const nsIntSize& aViewportSize) {
   MOZ_ASSERT(!mIgnoreInvalidation, "shouldn't be reentrant");
   mIgnoreInvalidation = true;
 
-  nsIntRect currentBounds;
+  LayoutDeviceIntRect currentBounds;
   mViewer->GetBounds(currentBounds);
 
   // If the bounds have changed, we need to do a layout flush.
-  if (currentBounds.Size() != aViewportSize) {
-    mViewer->SetBounds(IntRect(IntPoint(0, 0), aViewportSize));
+  if (currentBounds.Size().ToUnknownSize() != aViewportSize) {
+    mViewer->SetBounds(LayoutDeviceIntRect(
+        LayoutDeviceIntPoint(),
+        LayoutDeviceIntSize::FromUnknownSize(aViewportSize)));
     FlushLayout();
   }
 
@@ -207,7 +209,7 @@ SVGDocumentWrapper::OnStartRequest(nsIRequest* aRequest) {
     mViewer->GetDocument()->SetIsBeingUsedAsImage();
     StopAnimation();  // otherwise animations start automatically in helper doc
 
-    rv = mViewer->Init(nullptr, nsIntRect(0, 0, 0, 0), nullptr);
+    rv = mViewer->Init(nullptr, LayoutDeviceIntRect(), nullptr);
     if (NS_SUCCEEDED(rv)) {
       rv = mViewer->Open(nullptr, nullptr);
     }
diff --git a/layout/base/nsDocumentViewer.cpp b/layout/base/nsDocumentViewer.cpp
index f948cedba1b5..2e14057cd2e5 100644
--- a/layout/base/nsDocumentViewer.cpp
+++ b/layout/base/nsDocumentViewer.cpp
@@ -364,7 +364,7 @@ class nsDocumentViewer final : public nsIDocumentViewer,
    */
   nsresult InitInternal(nsIWidget* aParentWidget, nsISupports* aState,
                         mozilla::dom::WindowGlobalChild* aActor,
-                        const nsIntRect& aBounds, bool aDoCreation,
+                        const LayoutDeviceIntRect& aBounds, bool aDoCreation,
                         bool aNeedMakeCX = true,
                         bool aForceSetNewDocument = true);
   /**
@@ -434,7 +434,7 @@ class nsDocumentViewer final : public nsIDocumentViewer,
   nsIWidget* mParentWidget;  // purposely won't be ref counted.  May be null
   bool mAttachedToParent;    // view is attached to the parent widget
 
-  nsIntRect mBounds;
+  LayoutDeviceIntRect mBounds;
 
   int16_t mNumURLStarts;
   int16_t mDestroyBlockedCount;
@@ -673,7 +673,8 @@ nsDocumentViewer::GetContainer(nsIDocShell** aResult) {
 }
 
 NS_IMETHODIMP
-nsDocumentViewer::Init(nsIWidget* aParentWidget, const nsIntRect& aBounds,
+nsDocumentViewer::Init(nsIWidget* aParentWidget,
+                       const LayoutDeviceIntRect& aBounds,
                        WindowGlobalChild* aActor) {
   return InitInternal(aParentWidget, nullptr, aActor, aBounds, true);
 }
@@ -729,11 +730,10 @@ nsresult nsDocumentViewer::InitPresentationStuff(bool aDoInitialReflow) {
         p2a ==
         mPresContext->DeviceContext()->AppUnitsPerDevPixelAtUnitFullZoom());
 
-    nscoord width = p2a * mBounds.width;
-    nscoord height = p2a * mBounds.height;
+    const nsSize size = LayoutDevicePixel::ToAppUnits(mBounds.Size(), p2a);
 
-    mViewManager->SetWindowDimensions(width, height);
-    mPresContext->SetInitialVisibleArea(nsRect(0, 0, width, height));
+    mViewManager->SetWindowDimensions(size.width, size.height);
+    mPresContext->SetInitialVisibleArea(nsRect(nsPoint(), size));
     // We rely on the default zoom not being initialized until here.
     mPresContext->RecomputeBrowsingContextDependentData();
   }
@@ -796,8 +796,8 @@ static already_AddRefed<nsPresContext> CreatePresContext(
 // all the new objects or just initialize the existing ones
 nsresult nsDocumentViewer::InitInternal(
     nsIWidget* aParentWidget, nsISupports* aState, WindowGlobalChild* aActor,
-    const nsIntRect& aBounds, bool aDoCreation, bool aNeedMakeCX /*= true*/,
-    bool aForceSetNewDocument /* = true*/) {
+    const LayoutDeviceIntRect& aBounds, bool aDoCreation,
+    bool aNeedMakeCX /*= true*/, bool aForceSetNewDocument /* = true*/) {
   // We don't want any scripts to run here. That can cause flushing,
   // which can cause reentry into initialization of this document viewer,
   // which would be disastrous.
@@ -1883,7 +1883,7 @@ nsPresContext* nsDocumentViewer::GetPresContext() { return mPresContext; }
 nsViewManager* nsDocumentViewer::GetViewManager() { return mViewManager; }
 
 NS_IMETHODIMP
-nsDocumentViewer::GetBounds(nsIntRect& aResult) {
+nsDocumentViewer::GetBounds(LayoutDeviceIntRect& aResult) {
   NS_ENSURE_TRUE(mDocument, NS_ERROR_NOT_AVAILABLE);
   aResult = mBounds;
   return NS_OK;
@@ -1926,7 +1926,7 @@ void nsDocumentViewer::SetPreviousViewer(nsIDocumentViewer* aViewer) {
 }
 
 NS_IMETHODIMP
-nsDocumentViewer::SetBoundsWithFlags(const nsIntRect& aBounds,
+nsDocumentViewer::SetBoundsWithFlags(const LayoutDeviceIntRect& aBounds,
                                      uint32_t aFlags) {
   NS_ENSURE_TRUE(mDocument, NS_ERROR_NOT_AVAILABLE);
 
@@ -1963,13 +1963,12 @@ nsDocumentViewer::SetBoundsWithFlags(const nsIntRect& aBounds,
       // need to invalidate because what we want to draw to the screen has
       // changed.
       if (viewDims.width == width && viewDims.height == height) {
-        nsIFrame* f = rootView->GetFrame();
-        if (f) {
+        if (nsIFrame* f = rootView->GetFrame()) {
           f->InvalidateFrame();
 
           // Forcibly refresh the viewport sizes even if the view size is not
           // changed since it is possible that the |mBounds| change means that
-          // the software keyboard appeared/disappered, in such cases we might
+          // the software keyboard appeared/disappeared. In such cases we might
           // need to fire visual viewport events.
           mPresShell->RefreshViewportSize();
         }
@@ -1996,7 +1995,7 @@ nsDocumentViewer::SetBoundsWithFlags(const nsIntRect& aBounds,
 }
 
 NS_IMETHODIMP
-nsDocumentViewer::SetBounds(const nsIntRect& aBounds) {
+nsDocumentViewer::SetBounds(const LayoutDeviceIntRect& aBounds) {
   return SetBoundsWithFlags(aBounds, 0);
 }
 
@@ -2639,8 +2638,7 @@ MOZ_CAN_RUN_SCRIPT_BOUNDARY NS_IMETHODIMP nsDocumentViewer::GetContentSize(
   // Leave our viewport in a consistent state.
   {
     auto newBounds = LayoutDeviceIntRect::FromAppUnitsToOutside(
-                         shellArea, presContext->AppUnitsPerDevPixel())
-                         .ToUnknownRect();
+        shellArea, presContext->AppUnitsPerDevPixel());
     newBounds.MoveTo(mBounds.TopLeft());
     SetBounds(newBounds);
   }
diff --git a/layout/base/nsLayoutUtils.cpp b/layout/base/nsLayoutUtils.cpp
index 78e84d998477..6928a7e688fe 100644
--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -8022,7 +8022,7 @@ bool nsLayoutUtils::GetDocumentViewerSize(
     return false;
   }
 
-  nsIntRect bounds;
+  LayoutDeviceIntRect bounds;
   viewer->GetBounds(bounds);
 
   if (aPresContext->IsRootContentDocumentCrossProcess() &&
@@ -8038,7 +8038,7 @@ bool nsLayoutUtils::GetDocumentViewerSize(
     }
   }
 
-  aOutSize = LayoutDeviceIntRect::FromUnknownRect(bounds).Size();
+  aOutSize = bounds.Size();
   return true;
 }
 
diff --git a/layout/printing/nsPrintJob.cpp b/layout/printing/nsPrintJob.cpp
index 328a18ad5ec2..f4e528b4c1a0 100644
--- a/layout/printing/nsPrintJob.cpp
+++ b/layout/printing/nsPrintJob.cpp
@@ -1322,7 +1322,7 @@ nsresult nsPrintJob::ReflowPrintObject(const UniquePtr<nsPrintObject>& aPO) {
             do_QueryInterface(mDocViewerPrint)) {
       // If we're print-previewing and the top level document, use the bounds
       // from our doc viewer. Page bounds is not what we want.
-      nsIntRect bounds;
+      LayoutDeviceIntRect bounds;
       viewer->GetBounds(bounds);
       adjSize = nsSize(bounds.width * p2a, bounds.height * p2a);
     }