diff --git a/dom/base/DOMIntersectionObserver.cpp b/dom/base/DOMIntersectionObserver.cpp
index 6bf6339bcbcc..6f801bd5d3eb 100644
--- a/dom/base/DOMIntersectionObserver.cpp
+++ b/dom/base/DOMIntersectionObserver.cpp
@@ -14,6 +14,7 @@
 #include "nsRefreshDriver.h"
 #include "mozilla/PresShell.h"
 #include "mozilla/StaticPrefs_dom.h"
+#include "mozilla/StaticPrefs_layout.h"
 #include "mozilla/ServoBindings.h"
 #include "mozilla/dom/BrowserChild.h"
 #include "mozilla/dom/BrowsingContext.h"
@@ -150,6 +151,20 @@ static void LazyLoadCallback(
   }
 }
 
+static void ContentVisibilityCallback(
+    const Sequence<OwningNonNull<DOMIntersectionObserverEntry>>& aEntries) {
+  for (const auto& entry : aEntries) {
+    entry->Target()->SetVisibleForContentVisibility(entry->IsIntersecting());
+
+    if (RefPtr<Document> doc = entry->Target()->GetComposedDoc()) {
+      if (RefPtr<PresShell> presShell = doc->GetPresShell()) {
+        presShell->ScheduleContentRelevancyUpdate(
+            ContentRelevancyReason::Visible);
+      }
+    }
+  }
+}
+
 static LengthPercentage PrefMargin(float aValue, bool aIsPercentage) {
   return aIsPercentage ? LengthPercentage::FromPercentage(aValue / 100.0f)
                        : LengthPercentage::FromPixels(aValue);
@@ -182,6 +197,25 @@ DOMIntersectionObserver::CreateLazyLoadObserver(Document& aDocument) {
   return observer.forget();
 }
 
+already_AddRefed<DOMIntersectionObserver>
+DOMIntersectionObserver::CreateContentVisibilityObserver(Document& aDocument) {
+  RefPtr<DOMIntersectionObserver> observer =
+      new DOMIntersectionObserver(aDocument, ContentVisibilityCallback);
+
+  observer->mThresholds.AppendElement(0.0f);
+
+  auto margin = LengthPercentage::FromPercentage(
+      StaticPrefs::layout_css_content_visibility_relevant_content_margin() /
+      100.0f);
+
+  observer->mRootMargin.Get(eSideTop) = margin;
+  observer->mRootMargin.Get(eSideRight) = margin;
+  observer->mRootMargin.Get(eSideBottom) = margin;
+  observer->mRootMargin.Get(eSideLeft) = margin;
+
+  return observer.forget();
+}
+
 bool DOMIntersectionObserver::SetRootMargin(const nsACString& aString) {
   return Servo_IntersectionObserverRootMargin_Parse(&aString, &mRootMargin);
 }
diff --git a/dom/base/DOMIntersectionObserver.h b/dom/base/DOMIntersectionObserver.h
index ce985543af90..144e0ac4fea6 100644
--- a/dom/base/DOMIntersectionObserver.h
+++ b/dom/base/DOMIntersectionObserver.h
@@ -163,6 +163,9 @@ class DOMIntersectionObserver final : public nsISupports,
   static already_AddRefed<DOMIntersectionObserver>
   CreateLazyLoadObserverViewport(Document&);
 
+  static already_AddRefed<DOMIntersectionObserver>
+  CreateContentVisibilityObserver(Document&);
+
  protected:
   void Connect();
   void QueueIntersectionObserverEntry(Element* aTarget,
diff --git a/dom/base/Document.cpp b/dom/base/Document.cpp
index 7fcc9d34175b..fbca5e2e281f 100644
--- a/dom/base/Document.cpp
+++ b/dom/base/Document.cpp
@@ -2510,6 +2510,7 @@ NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INTERNAL(Document)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mLazyLoadImageObserver)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mLazyLoadImageObserverViewport)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mLastRememberedSizeObserver)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mContentVisibilityObserver)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mDOMImplementation)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mImageMaps)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mOrientationPendingPromise)
@@ -2628,6 +2629,7 @@ NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(Document)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mDisplayDocument)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mLazyLoadImageObserver)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mLazyLoadImageObserverViewport)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mContentVisibilityObserver)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mLastRememberedSizeObserver)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mFontFaceSet)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mReadyForIdle)
@@ -15767,6 +15769,24 @@ DOMIntersectionObserver& Document::EnsureLazyLoadImageObserver() {
   return *mLazyLoadImageObserver;
 }
 
+DOMIntersectionObserver& Document::EnsureContentVisibilityObserver() {
+  if (!mContentVisibilityObserver) {
+    mContentVisibilityObserver =
+        DOMIntersectionObserver::CreateContentVisibilityObserver(*this);
+  }
+  return *mContentVisibilityObserver;
+}
+
+void Document::ObserveForContentVisibility(Element& aElement) {
+  EnsureContentVisibilityObserver().Observe(aElement);
+}
+
+void Document::UnobserveForContentVisibility(Element& aElement) {
+  if (mContentVisibilityObserver) {
+    mContentVisibilityObserver->Unobserve(aElement);
+  }
+}
+
 ResizeObserver& Document::EnsureLastRememberedSizeObserver() {
   if (!mLastRememberedSizeObserver) {
     mLastRememberedSizeObserver =
diff --git a/dom/base/Document.h b/dom/base/Document.h
index d45ec95b66bd..abca2a83e8cc 100644
--- a/dom/base/Document.h
+++ b/dom/base/Document.h
@@ -3768,6 +3768,10 @@ class Document : public nsINode,
   }
   DOMIntersectionObserver& EnsureLazyLoadImageObserver();
 
+  DOMIntersectionObserver& EnsureContentVisibilityObserver();
+  void ObserveForContentVisibility(Element&);
+  void UnobserveForContentVisibility(Element&);
+
   ResizeObserver* GetLastRememberedSizeObserver() {
     return mLastRememberedSizeObserver;
   }
@@ -5137,6 +5141,10 @@ class Document : public nsINode,
   // Used to measure how effective the lazyload thresholds are.
   RefPtr<DOMIntersectionObserver> mLazyLoadImageObserverViewport;
 
+  // Used for detecting when `content-visibility: auto` elements are near
+  // or far from the viewport.
+  RefPtr<DOMIntersectionObserver> mContentVisibilityObserver;
+
   // ResizeObserver for storing and removing the last remembered size.
   // @see {@link https://drafts.csswg.org/css-sizing-4/#last-remembered}
   RefPtr<ResizeObserver> mLastRememberedSizeObserver;
diff --git a/dom/base/Element.cpp b/dom/base/Element.cpp
index 54b2d30eebbb..8de3a71a4c4c 100644
--- a/dom/base/Element.cpp
+++ b/dom/base/Element.cpp
@@ -724,7 +724,8 @@ bool Element::CheckVisibility(const CheckVisibilityOptions& aOptions) {
     return false;
   }
 
-  if (f->IsHiddenByContentVisibilityOnAnyAncestor()) {
+  if (f->IsHiddenByContentVisibilityOnAnyAncestor(
+          nsIFrame::IncludeContentVisibility::Hidden)) {
     // 2. If a shadow-including ancestor of this has content-visibility: hidden,
     // return false.
     return false;
diff --git a/dom/base/Element.h b/dom/base/Element.h
index d935d990af61..f146aa674f93 100644
--- a/dom/base/Element.h
+++ b/dom/base/Element.h
@@ -1333,6 +1333,29 @@ class Element : public FragmentOrElement {
     return GetLastRememberedISize().isSome();
   }
 
+  const Maybe<ContentRelevancy> GetContentRelevancy() const {
+    const auto* slots = GetExistingExtendedDOMSlots();
+    return slots ? slots->mContentRelevancy : Nothing();
+  }
+  void SetContentRelevancy(ContentRelevancy relevancy) {
+    ExtendedDOMSlots()->mContentRelevancy = Some(relevancy);
+  }
+
+  const Maybe<bool> GetVisibleForContentVisibility() const {
+    const auto* slots = GetExistingExtendedDOMSlots();
+    return slots ? slots->mVisibleForContentVisibility : Nothing();
+  }
+  void SetVisibleForContentVisibility(bool visible) {
+    ExtendedDOMSlots()->mVisibleForContentVisibility = Some(visible);
+  }
+
+  void ClearContentRelevancy() {
+    if (auto* slots = GetExistingExtendedDOMSlots()) {
+      slots->mContentRelevancy.reset();
+      slots->mVisibleForContentVisibility.reset();
+    }
+  }
+
   // https://drafts.csswg.org/cssom-view-1/#dom-element-checkvisibility
   MOZ_CAN_RUN_SCRIPT bool CheckVisibility(const CheckVisibilityOptions&);
 
diff --git a/dom/base/FragmentOrElement.h b/dom/base/FragmentOrElement.h
index 4e1ce720ca93..222b755ae20d 100644
--- a/dom/base/FragmentOrElement.h
+++ b/dom/base/FragmentOrElement.h
@@ -14,6 +14,7 @@
 #define FragmentOrElement_h___
 
 #include "mozilla/Attributes.h"
+#include "mozilla/EnumSet.h"
 #include "mozilla/MemoryReporting.h"
 #include "mozilla/UniquePtr.h"
 #include "nsCycleCollectionParticipant.h"  // NS_DECL_CYCLE_*
@@ -33,6 +34,8 @@ class nsIURI;
 
 namespace mozilla {
 class DeclarationBlock;
+enum class ContentRelevancyReason;
+using ContentRelevancy = EnumSet<ContentRelevancyReason, uint8_t>;
 namespace dom {
 struct CustomElementData;
 class Element;
@@ -198,6 +201,18 @@ class FragmentOrElement : public nsIContent {
      */
     Maybe<float> mLastRememberedBSize;
     Maybe<float> mLastRememberedISize;
+
+    /**
+     * Whether the content of this element is relevant for the purposes
+     * of `content-visibility: auto.
+     */
+    Maybe<ContentRelevancy> mContentRelevancy;
+
+    /**
+     * Whether the content of this element is considered visible for
+     * the purposes of `content-visibility: auto.
+     */
+    Maybe<bool> mVisibleForContentVisibility;
   };
 
   class nsDOMSlots : public nsIContent::nsContentSlots {
diff --git a/dom/base/Selection.cpp b/dom/base/Selection.cpp
index 5ff74d1a174c..45ac9935de22 100644
--- a/dom/base/Selection.cpp
+++ b/dom/base/Selection.cpp
@@ -9,6 +9,8 @@
  */
 
 #include "mozilla/dom/Selection.h"
+
+#include "LayoutConstants.h"
 #include "mozilla/intl/BidiEmbeddingLevel.h"
 
 #include "mozilla/AccessibleCaretEventHub.h"
@@ -3200,6 +3202,7 @@ void Selection::NotifySelectionListeners() {
   PresShell* presShell = GetPresShell();
   if (presShell) {
     doc = presShell->GetDocument();
+    presShell->ScheduleContentRelevancyUpdate(ContentRelevancyReason::Selected);
   }
 
   // We've notified all selection listeners even when some of them are removed
diff --git a/dom/base/nsFocusManager.cpp b/dom/base/nsFocusManager.cpp
index 0280ffc5fe69..f29523824dee 100644
--- a/dom/base/nsFocusManager.cpp
+++ b/dom/base/nsFocusManager.cpp
@@ -8,6 +8,7 @@
 
 #include "nsFocusManager.h"
 
+#include "LayoutConstants.h"
 #include "ChildIterator.h"
 #include "nsIInterfaceRequestorUtils.h"
 #include "nsGkAtoms.h"
@@ -2882,6 +2883,9 @@ void nsFocusManager::FireFocusOrBlurEvent(EventMessage aEventMessage,
   }
 #endif
 
+  aPresShell->ScheduleContentRelevancyUpdate(
+      ContentRelevancyReason::FocusInSubtree);
+
   nsContentUtils::AddScriptRunner(
       new FocusBlurEvent(aTarget, aEventMessage, aPresShell->GetPresContext(),
                          aWindowRaised, aIsRefocus, aRelatedTarget));
diff --git a/dom/base/nsRange.h b/dom/base/nsRange.h
index e58a9e4548f9..60bdd2bd738e 100644
--- a/dom/base/nsRange.h
+++ b/dom/base/nsRange.h
@@ -353,6 +353,18 @@ class nsRange final : public mozilla::dom::AbstractRange,
    */
   MOZ_CAN_RUN_SCRIPT void NotifySelectionListenersAfterRangeSet();
 
+  /**
+   * For a range for which IsInSelection() is true, return the closest common
+   * inclusive ancestor
+   * (https://dom.spec.whatwg.org/#concept-tree-inclusive-ancestor)
+   * for the range, which we had to compute when the common ancestor changed or
+   * IsInSelection became true, so we could register with it. That is, it's a
+   * faster version of GetClosestCommonInclusiveAncestor that only works for
+   * ranges in a Selection. The method will assert and the behavior is undefined
+   * if called on a range where IsInSelection() is false.
+   */
+  nsINode* GetRegisteredClosestCommonInclusiveAncestor();
+
  protected:
   /**
    * https://dom.spec.whatwg.org/#concept-tree-inclusive-ancestor
@@ -386,18 +398,6 @@ class nsRange final : public mozilla::dom::AbstractRange,
       const mozilla::RangeBoundaryBase<EPT, ERT>& aEndBoundary,
       nsINode* aRootNode, bool aNotInsertedYet = false);
 
-  /**
-   * For a range for which IsInSelection() is true, return the closest common
-   * inclusive ancestor
-   * (https://dom.spec.whatwg.org/#concept-tree-inclusive-ancestor)
-   * for the range, which we had to compute when the common ancestor changed or
-   * IsInSelection became true, so we could register with it. That is, it's a
-   * faster version of GetClosestCommonInclusiveAncestor that only works for
-   * ranges in a Selection. The method will assert and the behavior is undefined
-   * if called on a range where IsInSelection() is false.
-   */
-  nsINode* GetRegisteredClosestCommonInclusiveAncestor();
-
   // Assume that this is guaranteed that this is held by the caller when
   // this is used.  (Note that we cannot use AutoRestore for mCalledByJS
   // due to a bit field.)
diff --git a/layout/base/LayoutConstants.h b/layout/base/LayoutConstants.h
index bcdb51baea17..f441159fe3f2 100644
--- a/layout/base/LayoutConstants.h
+++ b/layout/base/LayoutConstants.h
@@ -92,6 +92,21 @@ inline constexpr nsSize kFallbackIntrinsicSize(kFallbackIntrinsicWidth,
  */
 enum class IntrinsicISizeType { MinISize, PrefISize };
 
+enum class ContentRelevancyReason {
+  // If the content of this Frame is on screen or nearly on screen.
+  Visible,
+
+  // If this Frame's element is a descendant of a top layer element.
+  DescendantOfTopLayerElement,
+
+  // If this Frame's element has focus in its subtree.
+  FocusInSubtree,
+
+  // If this Frame's content is part of a selection.
+  Selected,
+};
+using ContentRelevancy = EnumSet<ContentRelevancyReason, uint8_t>;
+
 }  // namespace mozilla
 
 #endif  // LayoutConstants_h___
diff --git a/layout/base/PresShell.cpp b/layout/base/PresShell.cpp
index e2f7204beb14..79d48700e683 100644
--- a/layout/base/PresShell.cpp
+++ b/layout/base/PresShell.cpp
@@ -2278,6 +2278,8 @@ void PresShell::NotifyDestroyingFrame(nsIFrame* aFrame) {
       mPendingScrollAnchorAdjustment.Remove(scrollableFrame);
       mPendingScrollResnap.Remove(scrollableFrame);
     }
+
+    mContentVisibilityAutoFrames.Remove(aFrame);
   }
 }
 
@@ -3661,6 +3663,18 @@ nsresult PresShell::ScrollContentIntoView(nsIContent* aContent,
     mContentToScrollTo = nullptr;
   }
 
+  // If the target frame is an ancestor of a `content-visibility: auto`
+  // element ensure that it is laid out, so that the boundary rectangle is
+  // correct.
+  if (mContentToScrollTo) {
+    if (nsIFrame* frame = mContentToScrollTo->GetPrimaryFrame()) {
+      if (frame->IsHiddenByContentVisibilityOnAnyAncestor(
+              nsIFrame::IncludeContentVisibility::Auto)) {
+        frame->PresShell()->EnsureReflowIfFrameHasHiddenContent(frame);
+      }
+    }
+  }
+
   // Flush layout and attempt to scroll in the process.
   if (PresShell* presShell = composedDoc->GetPresShell()) {
     presShell->SetNeedLayoutFlush();
@@ -3703,7 +3717,9 @@ void PresShell::DoScrollContentIntoView() {
   NS_ASSERTION(mDidInitialize, "should have done initial reflow by now");
 
   nsIFrame* frame = mContentToScrollTo->GetPrimaryFrame();
-  if (!frame || frame->IsHiddenByContentVisibilityOnAnyAncestor()) {
+
+  if (!frame || frame->IsHiddenByContentVisibilityOnAnyAncestor(
+                    nsIFrame::IncludeContentVisibility::Hidden)) {
     mContentToScrollTo->RemoveProperty(nsGkAtoms::scrolling);
     mContentToScrollTo = nullptr;
     return;
@@ -3730,10 +3746,6 @@ void PresShell::DoScrollContentIntoView() {
 bool PresShell::ScrollFrameIntoView(
     nsIFrame* aTargetFrame, const Maybe<nsRect>& aKnownRectRelativeToTarget,
     ScrollAxis aVertical, ScrollAxis aHorizontal, ScrollFlags aScrollFlags) {
-  if (aTargetFrame->IsHiddenByContentVisibilityOnAnyAncestor()) {
-    return false;
-  }
-
   // The scroll margin only applies to the whole bounds of the element, so don't
   // apply it if we get an arbitrary rect / point to scroll to.
   const nsMargin scrollMargin =
@@ -4271,6 +4283,13 @@ void PresShell::DoFlushPendingNotifications(mozilla::ChangesToFlush aFlush) {
    */
   FlushType flushType = aFlush.mFlushType;
 
+  // If this is a layout flush, first update the relevancy of any content
+  // of elements with `content-visibility: auto` so that the values
+  // returned from script queries are up-to-date.
+  if (flushType >= mozilla::FlushType::Layout) {
+    UpdateRelevancyOfContentVisibilityAutoFrames();
+  }
+
   MOZ_ASSERT(NeedFlush(flushType), "Why did we get called?");
 
   AUTO_PROFILER_MARKER_TEXT(
@@ -11898,3 +11917,28 @@ void PresShell::EnsureReflowIfFrameHasHiddenContent(nsIFrame* aFrame) {
 bool PresShell::IsForcingLayoutForHiddenContent(const nsIFrame* aFrame) const {
   return mHiddenContentInForcedLayout.Contains(aFrame->GetContent());
 }
+
+void PresShell::UpdateRelevancyOfContentVisibilityAutoFrames() {
+  if (mContentVisibilityRelevancyToUpdate.isEmpty()) {
+    return;
+  }
+
+  for (nsIFrame* frame : mContentVisibilityAutoFrames) {
+    frame->UpdateIsRelevantContent(mContentVisibilityRelevancyToUpdate);
+  }
+
+  mContentVisibilityRelevancyToUpdate.clear();
+}
+
+void PresShell::ScheduleContentRelevancyUpdate(ContentRelevancyReason aReason) {
+  if (MOZ_UNLIKELY(mIsDestroying)) {
+    return;
+  }
+
+  mContentVisibilityRelevancyToUpdate += aReason;
+
+  SetNeedLayoutFlush();
+  if (nsPresContext* presContext = GetPresContext()) {
+    presContext->RefreshDriver()->EnsureContentRelevancyUpdateHappens();
+  }
+}
diff --git a/layout/base/PresShell.h b/layout/base/PresShell.h
index 992a2fb29336..1c8d582342fd 100644
--- a/layout/base/PresShell.h
+++ b/layout/base/PresShell.h
@@ -13,6 +13,7 @@
 
 #include <stdio.h>  // for FILE definition
 #include "FrameMetrics.h"
+#include "LayoutConstants.h"
 #include "TouchManager.h"
 #include "Units.h"
 #include "Visibility.h"
@@ -1749,6 +1750,13 @@ class PresShell final : public nsStubDocumentObserver,
    */
   bool IsForcingLayoutForHiddenContent(const nsIFrame*) const;
 
+  void RegisterContentVisibilityAutoFrame(nsIFrame* aFrame) {
+    mContentVisibilityAutoFrames.Insert(aFrame);
+  }
+
+  void UpdateRelevancyOfContentVisibilityAutoFrames();
+  void ScheduleContentRelevancyUpdate(ContentRelevancyReason aReason);
+
  private:
   ~PresShell();
 
@@ -3009,6 +3017,12 @@ class PresShell final : public nsStubDocumentObserver,
 
   nsTHashSet<nsIContent*> mHiddenContentInForcedLayout;
 
+  nsTHashSet<nsIFrame*> mContentVisibilityAutoFrames;
+
+  // The type of content relevancy to update the next time content relevancy
+  // updates are triggered for `content-visibility: auto` frames.
+  ContentRelevancy mContentVisibilityRelevancyToUpdate;
+
   nsCallbackEventRequest* mFirstCallbackEventRequest = nullptr;
   nsCallbackEventRequest* mLastCallbackEventRequest = nullptr;
 
diff --git a/layout/base/nsRefreshDriver.cpp b/layout/base/nsRefreshDriver.cpp
index 5e10d5e7edda..2f278e0ed4ac 100644
--- a/layout/base/nsRefreshDriver.cpp
+++ b/layout/base/nsRefreshDriver.cpp
@@ -1339,6 +1339,7 @@ nsRefreshDriver::nsRefreshDriver(nsPresContext* aPresContext)
       mResizeSuppressed(false),
       mNotifyDOMContentFlushed(false),
       mNeedToUpdateIntersectionObservations(false),
+      mNeedToUpdateContentRelevancy(false),
       mInNormalTick(false),
       mAttemptedExtraTickSinceLastVsync(false),
       mHasExceededAfterLoadTickPeriod(false),
@@ -1938,6 +1939,9 @@ auto nsRefreshDriver::GetReasonsToTick() const -> TickReasons {
   if (mNeedToUpdateIntersectionObservations) {
     reasons |= TickReasons::eNeedsToUpdateIntersectionObservations;
   }
+  if (mNeedToUpdateContentRelevancy) {
+    reasons |= TickReasons::eNeedsToUpdateContentRelevancy;
+  }
   if (!mVisualViewportResizeEvents.IsEmpty()) {
     reasons |= TickReasons::eHasVisualViewportResizeEvents;
   }
@@ -1968,6 +1972,9 @@ void nsRefreshDriver::AppendTickReasonsToString(TickReasons aReasons,
   if (aReasons & TickReasons::eNeedsToUpdateIntersectionObservations) {
     aStr.AppendLiteral(" NeedsToUpdateIntersectionObservations");
   }
+  if (aReasons & TickReasons::eNeedsToUpdateContentRelevancy) {
+    aStr.AppendLiteral(" NeedsToUpdateContentRelevancy");
+  }
   if (aReasons & TickReasons::eHasVisualViewportResizeEvents) {
     aStr.AppendLiteral(" HasVisualViewportResizeEvents");
   }
@@ -2165,6 +2172,25 @@ void nsRefreshDriver::UpdateIntersectionObservations(TimeStamp aNowTime) {
   mNeedToUpdateIntersectionObservations = false;
 }
 
+void nsRefreshDriver::UpdateRelevancyOfContentVisibilityAutoFrames() {
+  if (!mNeedToUpdateContentRelevancy) {
+    return;
+  }
+
+  if (RefPtr<PresShell> topLevelPresShell = mPresContext->GetPresShell()) {
+    topLevelPresShell->UpdateRelevancyOfContentVisibilityAutoFrames();
+  }
+
+  mPresContext->Document()->EnumerateSubDocuments([](Document& aSubDoc) {
+    if (PresShell* presShell = aSubDoc.GetPresShell()) {
+      presShell->UpdateRelevancyOfContentVisibilityAutoFrames();
+    }
+    return CallState::Continue;
+  });
+
+  mNeedToUpdateContentRelevancy = false;
+}
+
 void nsRefreshDriver::DispatchAnimationEvents() {
   if (!mPresContext) {
     return;
@@ -2649,6 +2675,14 @@ void nsRefreshDriver::Tick(VsyncId aId, TimeStamp aNowTime,
     pm->UpdatePopupPositions(this);
   }
 
+  // Update the relevancy of the content of any `content-visibility: auto`
+  // elements. The specification says: "Specifically, such changes will
+  // take effect between steps 13 and 14 of Update the Rendering step of
+  // the Processing Model (between “run the animation frame callbacks” and
+  // “run the update intersection observations steps”)."
+  // https://drafts.csswg.org/css-contain/#cv-notes
+  UpdateRelevancyOfContentVisibilityAutoFrames();
+
   UpdateIntersectionObservations(aNowTime);
 
   /*
diff --git a/layout/base/nsRefreshDriver.h b/layout/base/nsRefreshDriver.h
index 4d9af9f4530d..aabc94a04836 100644
--- a/layout/base/nsRefreshDriver.h
+++ b/layout/base/nsRefreshDriver.h
@@ -417,6 +417,11 @@ class nsRefreshDriver final : public mozilla::layers::TransactionIdAllocator,
     mNeedToUpdateIntersectionObservations = true;
   }
 
+  void EnsureContentRelevancyUpdateHappens() {
+    EnsureTimerStarted();
+    mNeedToUpdateContentRelevancy = true;
+  }
+
   // Register a composition payload that will be forwarded to the layer manager
   // if the current or upcoming refresh tick does a paint.
   // If no paint happens, the payload is discarded.
@@ -429,9 +434,10 @@ class nsRefreshDriver final : public mozilla::layers::TransactionIdAllocator,
     eHasObservers = 1 << 0,
     eHasImageRequests = 1 << 1,
     eNeedsToUpdateIntersectionObservations = 1 << 2,
-    eHasVisualViewportResizeEvents = 1 << 3,
-    eHasScrollEvents = 1 << 4,
-    eHasVisualViewportScrollEvents = 1 << 5,
+    eNeedsToUpdateContentRelevancy = 1 << 3,
+    eHasVisualViewportResizeEvents = 1 << 4,
+    eHasScrollEvents = 1 << 5,
+    eHasVisualViewportScrollEvents = 1 << 6,
   };
 
   void AddForceNotifyContentfulPaintPresContext(nsPresContext* aPresContext);
@@ -473,6 +479,7 @@ class nsRefreshDriver final : public mozilla::layers::TransactionIdAllocator,
   MOZ_CAN_RUN_SCRIPT
   void RunFrameRequestCallbacks(mozilla::TimeStamp aNowTime);
   void UpdateIntersectionObservations(mozilla::TimeStamp aNowTime);
+  void UpdateRelevancyOfContentVisibilityAutoFrames();
 
   enum class IsExtraTick {
     No,
@@ -611,6 +618,10 @@ class nsRefreshDriver final : public mozilla::layers::TransactionIdAllocator,
   // all our documents.
   bool mNeedToUpdateIntersectionObservations : 1;
 
+  // True if we need to update the relevancy of `content-visibility: auto`
+  // elements in our documents.
+  bool mNeedToUpdateContentRelevancy : 1;
+
   // True if we're currently within the scope of Tick() handling a normal
   // (timer-driven) tick.
   bool mInNormalTick : 1;
diff --git a/layout/generic/ViewportFrame.cpp b/layout/generic/ViewportFrame.cpp
index 95e134297b7d..475b944bedfd 100644
--- a/layout/generic/ViewportFrame.cpp
+++ b/layout/generic/ViewportFrame.cpp
@@ -177,7 +177,8 @@ nsDisplayWrapList* ViewportFrame::BuildDisplayListForTopLayer(
       continue;
     }
 
-    if (frame->IsHiddenByContentVisibilityOnAnyAncestor()) {
+    if (frame->IsHiddenByContentVisibilityOnAnyAncestor(
+            nsIFrame::IncludeContentVisibility::Hidden)) {
       continue;
     }
 
diff --git a/layout/generic/nsIFrame.cpp b/layout/generic/nsIFrame.cpp
index 857ff5683198..e94f4b6900d2 100644
--- a/layout/generic/nsIFrame.cpp
+++ b/layout/generic/nsIFrame.cpp
@@ -46,6 +46,7 @@
 #include "nsCOMPtr.h"
 #include "nsFieldSetFrame.h"
 #include "nsFlexContainerFrame.h"
+#include "nsFocusManager.h"
 #include "nsFrameList.h"
 #include "nsPlaceholderFrame.h"
 #include "nsIBaseWindow.h"
@@ -381,7 +382,12 @@ bool nsIFrame::IsVisibleConsideringAncestors(uint32_t aFlags) const {
       return false;
     }
 
-    if (this != frame && frame->HidesContent()) {
+    // This method is used to determine if a frame is focusable, because it's
+    // called by nsIFrame::IsFocusable. `content-visibility: auto` should not
+    // force this frame to be unfocusable, so we only take into account
+    // `content-visibility: hidden` here.
+    if (this != frame &&
+        frame->HidesContent(IncludeContentVisibility::Hidden)) {
       return false;
     }
 
@@ -780,6 +786,16 @@ void nsIFrame::Init(nsIContent* aContent, nsContainerFrame* aParent,
     UpdateVisibleDescendantsState();
   }
 
+  if (disp->IsContentVisibilityAuto() &&
+      IsContentVisibilityPropertyApplicable()) {
+    PresShell()->RegisterContentVisibilityAutoFrame(this);
+    auto* element = Element::FromNodeOrNull(GetContent());
+    MOZ_ASSERT(element);
+    PresContext()->Document()->ObserveForContentVisibility(*element);
+  } else if (auto* element = Element::FromNodeOrNull(GetContent())) {
+    element->ClearContentRelevancy();
+  }
+
   // TODO(mrobinson): Once bug 1765615 is fixed, this should be called on
   // layout changes. In addition, when `content-visibility: auto` is implemented
   // this should also be called when scrolling or focus causes content to be
@@ -855,6 +871,13 @@ void nsIFrame::DestroyFrom(nsIFrame* aDestructRoot,
     }
   }
 
+  if (disp->IsContentVisibilityAuto() &&
+      IsContentVisibilityPropertyApplicable()) {
+    if (auto* element = Element::FromNodeOrNull(GetContent())) {
+      PresContext()->Document()->UnobserveForContentVisibility(*element);
+    }
+  }
+
   // Disable visibility tracking. Note that we have to do this before we clear
   // frame properties and lose track of whether we were previously visible.
   // XXX(seth): It'd be ideal to assert that we're already marked nonvisible
@@ -6832,12 +6855,53 @@ bool nsIFrame::IsContentDisabled() const {
   return element && element->IsDisabled();
 }
 
-bool nsIFrame::HidesContent() const {
-  if (!StyleDisplay()->IsContentVisibilityHidden()) {
+bool nsIFrame::IsContentVisibilityPropertyApplicable() const {
+  return GetContent() && GetContent()->IsElement() &&
+         (!StyleDisplay()->IsInlineFlow() ||
+          IsFrameOfType(nsIFrame::eReplaced));
+}
+
+bool nsIFrame::IsContentRelevant() const {
+  MOZ_ASSERT(IsContentVisibilityPropertyApplicable());
+  MOZ_ASSERT(StyleDisplay()->IsContentVisibilityAuto());
+
+  auto* element = Element::FromNodeOrNull(GetContent());
+  MOZ_ASSERT(element);
+
+  Maybe<ContentRelevancy> relevancy = element->GetContentRelevancy();
+  if (relevancy.isSome()) {
+    return !relevancy->isEmpty();
+  }
+
+  // If there is no relevancy set, then this frame still has not received had
+  // the initial visibility callback call. In that case, only rely on whether
+  // or not it is inside a top layer element which will never change for this
+  // frame and allows proper rendering of the top layer.
+  return IsDescendantOfTopLayerElement();
+}
+
+bool nsIFrame::HidesContent(
+    const EnumSet<IncludeContentVisibility>& aInclude) const {
+  const auto& disp = *StyleDisplay();
+  if (disp.IsContentVisibilityVisible()) {
+    return false;
+  };
+
+  if (!IsContentVisibilityPropertyApplicable()) {
     return false;
   }
 
-  return IsFrameOfType(nsIFrame::eReplaced) || !StyleDisplay()->IsInlineFlow();
+  if (aInclude.contains(IncludeContentVisibility::Hidden) &&
+      disp.IsContentVisibilityHidden()) {
+    return true;
+  }
+
+  if (aInclude.contains(IncludeContentVisibility::Auto) &&
+      disp.IsContentVisibilityAuto()) {
+    return !IsContentRelevant();
+  }
+
+  return false;
 }
 
 bool nsIFrame::HidesContentForLayout() const {
@@ -6850,7 +6914,8 @@ bool nsIFrame::IsHiddenByContentVisibilityOfInFlowParentForLayout() const {
          !(Style()->IsAnonBox() && !IsFrameOfType(nsIFrame::eLineParticipant));
 }
 
-bool nsIFrame::IsHiddenByContentVisibilityOnAnyAncestor() const {
+bool nsIFrame::IsHiddenByContentVisibilityOnAnyAncestor(
+    const EnumSet<IncludeContentVisibility>& aInclude) const {
   if (!StaticPrefs::layout_css_content_visibility_enabled()) {
     return false;
   }
@@ -6858,7 +6923,7 @@ bool nsIFrame::IsHiddenByContentVisibilityOnAnyAncestor() const {
   bool isAnonymousBlock =
       Style()->IsAnonBox() && !IsFrameOfType(nsIFrame::eLineParticipant);
   for (nsIFrame* cur = GetInFlowParent(); cur; cur = cur->GetInFlowParent()) {
-    if (!isAnonymousBlock && cur->HidesContent()) {
+    if (!isAnonymousBlock && cur->HidesContent(aInclude)) {
       return true;
     }
 
@@ -6871,6 +6936,111 @@ bool nsIFrame::IsHiddenByContentVisibilityOnAnyAncestor() const {
   return false;
 }
 
+bool nsIFrame::HasSelectionInSubtree() {
+  if (IsSelected()) {
+    return true;
+  }
+
+  RefPtr<nsFrameSelection> frameSelection = GetFrameSelection();
+  const Selection* selection =
+      frameSelection->GetSelection(SelectionType::eNormal);
+  if (!selection) {
+    return false;
+  }
+
+  for (uint32_t i = 0; i < selection->RangeCount(); i++) {
+    auto* range = selection->GetRangeAt(i);
+    MOZ_ASSERT(range);
+
+    const auto* commonAncestorNode =
+        range->GetRegisteredClosestCommonInclusiveAncestor();
+    if (commonAncestorNode->IsInclusiveDescendantOf(GetContent())) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+bool nsIFrame::IsDescendantOfTopLayerElement() const {
+  if (!GetContent()) {
+    return false;
+  }
+
+  nsTArray<dom::Element*> topLayer = PresContext()->Document()->GetTopLayer();
+  for (auto* element : topLayer) {
+    if (GetContent()->IsInclusiveFlatTreeDescendantOf(element)) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+void nsIFrame::UpdateIsRelevantContent(
+    const ContentRelevancy& aRelevancyToUpdate) {
+  MOZ_ASSERT(IsContentVisibilityPropertyApplicable());
+  MOZ_ASSERT(StyleDisplay()->IsContentVisibilityAuto());
+
+  auto* element = Element::FromNodeOrNull(GetContent());
+  MOZ_ASSERT(element);
+
+  ContentRelevancy newRelevancy;
+  Maybe<ContentRelevancy> oldRelevancy = element->GetContentRelevancy();
+  if (oldRelevancy.isSome()) {
+    newRelevancy = *oldRelevancy;
+  }
+
+  auto setRelevancyValue = [&](ContentRelevancyReason reason, bool value) {
+    if (value) {
+      newRelevancy += reason;
+    } else {
+      newRelevancy -= reason;
+    }
+  };
+
+  if (!oldRelevancy ||
+      aRelevancyToUpdate.contains(ContentRelevancyReason::Visible)) {
+    Maybe<bool> visible = element->GetVisibleForContentVisibility();
+    if (visible.isSome()) {
+      setRelevancyValue(ContentRelevancyReason::Visible, *visible);
+    }
+  }
+
+  if (!oldRelevancy ||
+      aRelevancyToUpdate.contains(ContentRelevancyReason::FocusInSubtree)) {
+    setRelevancyValue(ContentRelevancyReason::FocusInSubtree,
+                      element->State().HasAtLeastOneOfStates(
+                          ElementState::FOCUS_WITHIN | ElementState::FOCUS));
+  }
+
+  if (!oldRelevancy ||
+      aRelevancyToUpdate.contains(ContentRelevancyReason::Selected)) {
+    setRelevancyValue(ContentRelevancyReason::Selected,
+                      HasSelectionInSubtree());
+  }
+
+  if (!oldRelevancy ||
+      aRelevancyToUpdate.contains(
+          ContentRelevancyReason::DescendantOfTopLayerElement)) {
+    setRelevancyValue(ContentRelevancyReason::DescendantOfTopLayerElement,
+                      IsDescendantOfTopLayerElement());
+  }
+
+  bool overallRelevancyChanged =
+      !oldRelevancy || oldRelevancy->isEmpty() != newRelevancy.isEmpty();
+  if (!oldRelevancy || *oldRelevancy != newRelevancy) {
+    element->SetContentRelevancy(newRelevancy);
+  }
+
+  if (overallRelevancyChanged) {
+    HandleLastRememberedSize();
+    PresShell()->FrameNeedsReflow(this, IntrinsicDirty::StyleChange,
+                                  NS_FRAME_IS_DIRTY);
+    InvalidateFrame();
+  }
+}
+
 nsresult nsIFrame::CharacterDataChanged(const CharacterDataChangeInfo&) {
   MOZ_ASSERT_UNREACHABLE("should only be called for text frames");
   return NS_OK;
diff --git a/layout/generic/nsIFrame.h b/layout/generic/nsIFrame.h
index bc4de570467b..d34d1d64a58a 100644
--- a/layout/generic/nsIFrame.h
+++ b/layout/generic/nsIFrame.h
@@ -536,6 +536,7 @@ class nsIFrame : public nsQueryFrame {
   using ReflowOutput = mozilla::ReflowOutput;
   using Visibility = mozilla::Visibility;
   using LengthPercentage = mozilla::LengthPercentage;
+  using ContentRelevancy = mozilla::ContentRelevancy;
 
   using nsDisplayItem = mozilla::nsDisplayItem;
   using nsDisplayList = mozilla::nsDisplayList;
@@ -3180,11 +3181,34 @@ class nsIFrame : public nsQueryFrame {
    */
   bool IsContentDisabled() const;
 
+  /**
+   * Whether the content-visibility CSS property applies to this frame.
+   */
+  bool IsContentVisibilityPropertyApplicable() const;
+
+  enum class IncludeContentVisibility {
+    Auto,
+    Hidden,
+  };
+
+  constexpr static mozilla::EnumSet<IncludeContentVisibility>
+  IncludeAllContentVisibility() {
+    return {IncludeContentVisibility::Auto, IncludeContentVisibility::Hidden};
+  }
+
+  /**
+   * Returns true if this frame's `content-visibility: auto` element is
+   * considered relevant content.
+   */
+  bool IsContentRelevant() const;
+
   /**
    * Whether this frame hides its contents via the `content-visibility`
    * property.
+   * @param aInclude specifies what kind of `content-visibility` to include.
    */
-  bool HidesContent() const;
+  bool HidesContent(const mozilla::EnumSet<IncludeContentVisibility>& =
+                        IncludeAllContentVisibility()) const;
 
   /**
    * Whether this frame hides its contents via the `content-visibility`
@@ -3197,8 +3221,11 @@ class nsIFrame : public nsQueryFrame {
   /**
    * Returns true if this frame is entirely hidden due the `content-visibility`
    * property on an ancestor.
+   * @param aInclude specifies what kind of `content-visibility` to include.
    */
-  bool IsHiddenByContentVisibilityOnAnyAncestor() const;
+  bool IsHiddenByContentVisibilityOnAnyAncestor(
+      const mozilla::EnumSet<IncludeContentVisibility>& =
+          IncludeAllContentVisibility()) const;
 
   /**
    * Returns true is this frame is hidden by its first unskipped in flow
@@ -3206,6 +3233,27 @@ class nsIFrame : public nsQueryFrame {
    */
   bool IsHiddenByContentVisibilityOfInFlowParentForLayout() const;
 
+  /**
+   * Whether or not this frame's content is a descendant of a top layer element
+   * used to determine if this frame is relevant content for
+   * `content-visibility: auto`.
+   */
+  bool IsDescendantOfTopLayerElement() const;
+
+  /**
+   * Returns true if this frame has a SelectionType::eNormal type selection in
+   * somewhere in its subtree of frames. This is used to determine content
+   * relevancy for `content-visibility: auto`.
+   */
+  bool HasSelectionInSubtree();
+
+  /**
+   * Update the whether or not this frame is considered relevant content for the
+   * purposes of `content-visibility: auto` according to the rules specified in
+   * https://drafts.csswg.org/css-contain-2/#relevant-to-the-user.
+   */
+  void UpdateIsRelevantContent(const ContentRelevancy& aRelevancyToUpdate);
+
   /**
    * Get the "type" of the frame.
    *
diff --git a/layout/style/nsStyleStruct.h b/layout/style/nsStyleStruct.h
index e943fee81b5c..f9ec4319a6f5 100644
--- a/layout/style/nsStyleStruct.h
+++ b/layout/style/nsStyleStruct.h
@@ -1612,6 +1612,10 @@ struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleDisplay {
     return mContentVisibility == StyleContentVisibility::Hidden;
   }
 
+  bool IsContentVisibilityAuto() const {
+    return mContentVisibility == StyleContentVisibility::Auto;
+  }
+
   /* Returns whether the element has the transform property or a related
    * property. */
   bool HasTransformStyle() const {
diff --git a/modules/libpref/init/StaticPrefList.yaml b/modules/libpref/init/StaticPrefList.yaml
index b1f478bd91c7..06bf47864d87 100644
--- a/modules/libpref/init/StaticPrefList.yaml
+++ b/modules/libpref/init/StaticPrefList.yaml
@@ -8655,6 +8655,12 @@
   value: true
   mirror: always
 
+# The margin used for detecting relevancy for `content-visibility: auto`.
+- name: layout.css.content-visibility-relevant-content-margin
+  type: float
+  value: 50 # 50%
+  mirror: always
+
 # Whether to block large cursors intersecting UI.
 - name: layout.cursor.block.enabled
   type: bool
diff --git a/testing/web-platform/meta/css/css-contain/__dir__.ini b/testing/web-platform/meta/css/css-contain/__dir__.ini
index d828a91efd16..4bc61b00f24e 100644
--- a/testing/web-platform/meta/css/css-contain/__dir__.ini
+++ b/testing/web-platform/meta/css/css-contain/__dir__.ini
@@ -1,2 +1,2 @@
-prefs: [layout.css.content-visibility.enabled:true]
+prefs: [layout.css.content-visibility.enabled:true, layout.css.contain-intrinsic-size.enabled:true]
 leak-threshold: [rdd:51200]
diff --git a/testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-058.html.ini b/testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-058.html.ini
new file mode 100644
index 000000000000..0f634857b51e
--- /dev/null
+++ b/testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-058.html.ini
@@ -0,0 +1,3 @@
+[content-visibility-058.html]
+  bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1797467
+  expected: FAIL
diff --git a/testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-064.html.ini b/testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-064.html.ini
index 7b1e2b6e3555..0100d6fd864a 100644
--- a/testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-064.html.ini
+++ b/testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-064.html.ini
@@ -1,3 +1,3 @@
 [content-visibility-064.html]
-  fuzzy:
-    if os == "mac": maxDifference=0-11;totalPixels=0-44
+  bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1800868
+  expected: FAIL
diff --git a/testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-068.html.ini b/testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-068.html.ini
index 3a753f59dbb7..fedc6eb1ee78 100644
--- a/testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-068.html.ini
+++ b/testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-068.html.ini
@@ -2,4 +2,5 @@
   expected:
     if (os == "android") and fission: [OK, TIMEOUT]
   [Content Visibility: off-screen focus]
+    bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1797447
     expected: FAIL
diff --git a/testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-069.html.ini b/testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-069.html.ini
deleted file mode 100644
index be5eafa0a150..000000000000
--- a/testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-069.html.ini
+++ /dev/null
@@ -1,3 +0,0 @@
-[content-visibility-069.html]
-  expected:
-    if (os == "android") and fission: [OK, TIMEOUT]
diff --git a/testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-070.html.ini b/testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-070.html.ini
deleted file mode 100644
index 9071ecaf135c..000000000000
--- a/testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-070.html.ini
+++ /dev/null
@@ -1,5 +0,0 @@
-[content-visibility-070.html]
-  expected:
-    if (os == "android") and fission: [OK, TIMEOUT]
-  [Content Visibility: off-screen selection]
-    expected: FAIL
diff --git a/testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-071.html.ini b/testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-071.html.ini
deleted file mode 100644
index 1bd7702bdfd6..000000000000
--- a/testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-071.html.ini
+++ /dev/null
@@ -1,20 +0,0 @@
-[content-visibility-071.html]
-  expected:
-    if (os == "android") and fission: [OK, TIMEOUT]
-  [Range flipped from back to front: ]
-    expected: FAIL
-
-  [Range goes back and forth: ]
-    expected: FAIL
-
-  [Range flipped from front to back: ]
-    expected: FAIL
-
-  [Range shrunk to cover fewer elements: ]
-    expected: FAIL
-
-  [Range extended to cover more elements: ]
-    expected: FAIL
-
-  [One elements selected: ]
-    expected: FAIL
diff --git a/testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-072.html.ini b/testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-072.html.ini
deleted file mode 100644
index 6cf1cea75d48..000000000000
--- a/testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-072.html.ini
+++ /dev/null
@@ -1,12 +0,0 @@
-[content-visibility-072.html]
-  [two.getBoundingClientRect(): ]
-    expected: FAIL
-
-  [three.getBoundingClientRect(): ]
-    expected: FAIL
-
-  [four.getBoundingClientRect(): ]
-    expected: FAIL
-
-  [five.getBoundingClientRect(): ]
-    expected: FAIL
diff --git a/testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-with-top-layer-005.html.ini b/testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-with-top-layer-005.html.ini
new file mode 100644
index 000000000000..f94a157f54dc
--- /dev/null
+++ b/testing/web-platform/meta/css/css-contain/content-visibility/content-visibility-with-top-layer-005.html.ini
@@ -0,0 +1,3 @@
+[content-visibility-with-top-layer-005.html]
+  fuzzy:
+    if os == "win": maxDifference=0-92;totalPixels=0-2
diff --git a/testing/web-platform/meta/css/css-sizing/contain-intrinsic-size/auto-003.html.ini b/testing/web-platform/meta/css/css-sizing/contain-intrinsic-size/auto-003.html.ini
deleted file mode 100644
index 605e849d475d..000000000000
--- a/testing/web-platform/meta/css/css-sizing/contain-intrinsic-size/auto-003.html.ini
+++ /dev/null
@@ -1,5 +0,0 @@
-[auto-003.html]
-  expected:
-    if (os == "android") and fission: [OK, TIMEOUT]
-  [contain-intrinsic-size: auto]
-    expected: FAIL
diff --git a/testing/web-platform/meta/css/css-sizing/contain-intrinsic-size/auto-012.html.ini b/testing/web-platform/meta/css/css-sizing/contain-intrinsic-size/auto-012.html.ini
deleted file mode 100644
index 1999d9b8b077..000000000000
--- a/testing/web-platform/meta/css/css-sizing/contain-intrinsic-size/auto-012.html.ini
+++ /dev/null
@@ -1,5 +0,0 @@
-[auto-012.html]
-  [Still sizing with last remembered size]
-    expected: FAIL
-  [Sizing with new last remembered size]
-    expected: FAIL
diff --git a/testing/web-platform/tests/css/css-contain/content-visibility/content-visibility-070.html b/testing/web-platform/tests/css/css-contain/content-visibility/content-visibility-070.html
index 4f63069edde4..a41b513e6269 100644
--- a/testing/web-platform/tests/css/css-contain/content-visibility/content-visibility-070.html
+++ b/testing/web-platform/tests/css/css-contain/content-visibility/content-visibility-070.html
@@ -59,8 +59,8 @@ async_test((t) => {
   function step2() {
     const r = container.getBoundingClientRect();
     t.step(() => {
-      assert_equals(r.y, 3000, "step3 offset");
-      assert_equals(r.height, 10, "step3 height");
+      assert_equals(r.y, 3000, "step2 offset");
+      assert_equals(r.height, 10, "step2 height");
     });
     document.scrollingElement.scrollTop = 3000;
     requestAnimationFrame(step3);
@@ -69,8 +69,8 @@ async_test((t) => {
   function step3() {
     const r = container.getBoundingClientRect();
     t.step(() => {
-      assert_less_than(r.y, 3000, "step2 offset");
-      assert_equals(r.height, 10, "step2 height");
+      assert_less_than(r.y, 3000, "step3 offset");
+      assert_equals(r.height, 10, "step3 height");
     });
     document.scrollingElement.scrollTop = 0;
     requestAnimationFrame(step4);
@@ -88,8 +88,8 @@ async_test((t) => {
   function step5() {
     const r = container.getBoundingClientRect();
     t.step(() => {
-      assert_equals(r.y, 3000, "step4 offset");
-      assert_equals(r.height, 10, "step4 height");
+      assert_equals(r.y, 3000, "step5 offset");
+      assert_equals(r.height, 10, "step5 height");
     });
 
     selection.removeAllRanges();
diff --git a/testing/web-platform/tests/css/css-contain/content-visibility/content-visibility-auto-in-iframe-ref.html b/testing/web-platform/tests/css/css-contain/content-visibility/content-visibility-auto-in-iframe-ref.html
new file mode 100644
index 000000000000..03a2875b75a7
--- /dev/null
+++ b/testing/web-platform/tests/css/css-contain/content-visibility/content-visibility-auto-in-iframe-ref.html
@@ -0,0 +1,25 @@
+<!doctype HTML>
+<html>
+<meta charset="utf8">
+<title>CSS Content Visibility: auto container in an iframe (reference)</title>
+<link rel="author" title="Martin Robinson" href="mailto:mrobinson@igalia.com">
+<link rel="help" href="https://drafts.csswg.org/css-contain/#content-visibility">
+
+<iframe id="frame" srcdoc='
+  <style>
+  #container {
+    width: 200px;
+    height: 200px;
+  }
+  #child {
+    width: 100px;
+    height: 100px;
+    background: green;
+  }
+  </style>
+  <div id="container">
+    <div id="child"></div>
+  </div>
+  hello
+'></iframe>
+</html>
diff --git a/testing/web-platform/tests/css/css-contain/content-visibility/content-visibility-auto-in-iframe.html b/testing/web-platform/tests/css/css-contain/content-visibility/content-visibility-auto-in-iframe.html
new file mode 100644
index 000000000000..ba02cac6684d
--- /dev/null
+++ b/testing/web-platform/tests/css/css-contain/content-visibility/content-visibility-auto-in-iframe.html
@@ -0,0 +1,28 @@
+<!doctype HTML>
+<html>
+<meta charset="utf8">
+<title>CSS Content Visibility: auto container in an iframe</title>
+<link rel="author" title="Martin Robinson" href="mailto:mrobinson@igalia.com">
+<link rel="help" href="https://drafts.csswg.org/css-contain/#content-visibility">
+<link rel="match" href="content-visibility-auto-in-iframe-ref.html">
+<meta name="assert" content="content-visibility: auto shows on screen iframe contents">
+
+<iframe id="frame" srcdoc='
+  <style>
+  #container {
+    width: 200px;
+    height: 200px;
+    content-visibility: auto;
+  }
+  #child {
+    width: 100px;
+    height: 100px;
+    background: green;
+  }
+  </style>
+  <div id="container">
+    <div id="child"></div>
+  </div>
+  hello
+'></iframe>
+</html>
diff --git a/testing/web-platform/tests/css/css-contain/content-visibility/content-visibility-auto-intrinsic-width.html b/testing/web-platform/tests/css/css-contain/content-visibility/content-visibility-auto-intrinsic-width.html
new file mode 100644
index 000000000000..bd90fff5143e
--- /dev/null
+++ b/testing/web-platform/tests/css/css-contain/content-visibility/content-visibility-auto-intrinsic-width.html
@@ -0,0 +1,25 @@
+<!doctype HTML>
+<html>
+<meta charset="utf8">
+<title>Content Visibility: Elements with content-visibility: auto and intrinsic width should render correctly</title>
+<link rel="author" title="Martin Robinson" href="mailto:mrobinson@igalia.com">
+<link rel="help" href="https://drafts.csswg.org/css-contain/#content-visibility">
+<link rel="match" href="container-ref.html">
+<meta name="assert" content="Elements with content-visibility: auto and intrinsic width should render correctly">
+
+<style>
+#container {
+  content-visibility: auto;
+  width: max-content;
+  background: lightblue;
+}
+
+#child {
+  width: 150px;
+  height: 150px;
+}
+</style>
+
+<div id="container">
+    <div id="child"></div>
+</div>
diff --git a/testing/web-platform/tests/css/css-contain/content-visibility/content-visibility-with-top-layer-005.html b/testing/web-platform/tests/css/css-contain/content-visibility/content-visibility-with-top-layer-005.html
new file mode 100644
index 000000000000..5283aea19734
--- /dev/null
+++ b/testing/web-platform/tests/css/css-contain/content-visibility/content-visibility-with-top-layer-005.html
@@ -0,0 +1,31 @@
+<!doctype html>
+<html class="reftest-wait">
+<meta charset="utf8">
+<title>CSS Content Visibility: dialog shows under c-v auto</title>
+<link rel="author" title="Martin Robinson" href="mailto:mrobinson@igalia.com">
+<link rel="help" href="https://drafts.csswg.org/css-contain/#content-visibility">
+<link rel="match" href="spacer-with-top-layer-ref.html">
+<meta name="assert" content="top layer dialogs render under c-v auto">
+
+<script src="/common/reftest-wait.js"></script>
+
+<style>
+.box { width: 100px; height: 100px; border: 1px solid black; }
+.auto { content-visibility: auto }
+.spacer { width: 10px; height: 3000px; background: lightblue; }
+</style>
+
+<div class=spacer></div>
+<div id=container class="box">
+content
+<dialog id=dialog><div id=inner class="auto">PASS</div></dialog>
+</div>
+
+<script>
+function runTest() {
+  dialog.showModal();
+  takeScreenshot();
+}
+
+onload = () => requestAnimationFrame(() => requestAnimationFrame(runTest));
+</script>
diff --git a/toolkit/components/find/nsFind.cpp b/toolkit/components/find/nsFind.cpp
index 27d4b9775480..3328db506330 100644
--- a/toolkit/components/find/nsFind.cpp
+++ b/toolkit/components/find/nsFind.cpp
@@ -143,8 +143,9 @@ static bool IsVisibleNode(const nsINode* aNode) {
     return true;
   }
 
-  if (frame->HidesContent() ||
-      frame->IsHiddenByContentVisibilityOnAnyAncestor()) {
+  if (frame->HidesContent(nsIFrame::IncludeContentVisibility::Hidden) ||
+      frame->IsHiddenByContentVisibilityOnAnyAncestor(
+          nsIFrame::IncludeContentVisibility::Hidden)) {
     return false;
   }