Backed out changeset 2f74f8f2ed19 (bug 1689816) for causing reftest failures on skip-ink-multiline-position.html.

accessible/base/nsAccessibilityService.cpp

@@ -75,6 +75,7 @@
 #include "mozilla/Services.h"
 #include "mozilla/StaticPrefs_accessibility.h"
 #include "mozilla/SVGGeometryFrame.h"
+#include "nsDeckFrame.h"
 
 #include "XULAlertAccessible.h"
 #include "XULComboboxAccessible.h"
@@ -442,20 +443,63 @@ LocalAccessible* nsAccessibilityService::GetRootDocumentAccessible(
   return nullptr;
 }
 
-void nsAccessibilityService::NotifyOfTabPanelVisibilityChange(
-    PresShell* aPresShell, Element* aPanel, bool aNowVisible) {
-  MOZ_ASSERT(aPanel->GetParent()->IsXULElement(nsGkAtoms::tabpanels));
-
+void nsAccessibilityService::DeckPanelSwitched(PresShell* aPresShell,
+                                               nsIContent* aDeckNode,
+                                               nsIFrame* aPrevBoxFrame,
+                                               nsIFrame* aCurrentBoxFrame) {
   DocAccessible* document = GetDocAccessible(aPresShell);
   if (!document) {
     return;
   }
+  // A deck with a LocalAccessible is a tabpanels element.
+  const bool isTabPanels = document->HasAccessible(aDeckNode);
+  MOZ_ASSERT(!isTabPanels || aDeckNode->IsXULElement(nsGkAtoms::tabpanels),
+             "A deck with a LocalAccessible should be a tabpanels element");
 
-  if (LocalAccessible* acc = document->GetAccessible(aPanel)) {
+  if (aPrevBoxFrame) {
+    nsIContent* panelNode = aPrevBoxFrame->GetContent();
+#ifdef A11Y_LOG
+    if (logging::IsEnabled(logging::eTree)) {
+      logging::MsgBegin("TREE", "deck panel unselected");
+      logging::Node("container", panelNode);
+      logging::Node("content", aDeckNode);
+      logging::MsgEnd();
+    }
+#endif
+    if (isTabPanels) {
+      // Tabpanels are accessible even when not selected.
+      if (LocalAccessible* acc = document->GetAccessible(panelNode)) {
         RefPtr<AccEvent> event =
-        new AccStateChangeEvent(acc, states::OFFSCREEN, aNowVisible);
+            new AccStateChangeEvent(acc, states::OFFSCREEN, true);
         document->FireDelayedEvent(event);
       }
+    } else {
+      document->ContentRemoved(panelNode);
+    }
+  }
+
+  if (aCurrentBoxFrame) {
+    nsIContent* panelNode = aCurrentBoxFrame->GetContent();
+#ifdef A11Y_LOG
+    if (logging::IsEnabled(logging::eTree)) {
+      logging::MsgBegin("TREE", "deck panel selected");
+      logging::Node("container", panelNode);
+      logging::Node("content", aDeckNode);
+      logging::MsgEnd();
+    }
+#endif
+    if (isTabPanels) {
+      // Tabpanels are accessible even when not selected, so we don't have to
+      // insert a LocalAccessible.
+      if (LocalAccessible* acc = document->GetAccessible(panelNode)) {
+        RefPtr<AccEvent> event =
+            new AccStateChangeEvent(acc, states::OFFSCREEN, false);
+        document->FireDelayedEvent(event);
+      }
+    } else {
+      document->ContentInserted(panelNode, panelNode->GetNextSibling());
+    }
+  }
 }
 
 void nsAccessibilityService::ContentRangeInserted(PresShell* aPresShell,
@@ -1084,6 +1128,16 @@ LocalAccessible* nsAccessibilityService::CreateAccessible(
 
   // XUL accessibles.
   if (!newAcc && content->IsXULElement()) {
+    // No accessible for not selected deck panel and its children.
+    if (!aContext->IsXULTabpanels()) {
+      nsDeckFrame* deckFrame = do_QueryFrame(frame->GetParent());
+      if (deckFrame && deckFrame->GetSelectedBox() != frame) {
+        if (aIsSubtreeHidden) *aIsSubtreeHidden = true;
+
+        return nullptr;
+      }
+    }
+
     if (content->IsXULElement(nsGkAtoms::panel)) {
       // We filter here instead of in the XUL map because
       // if we filter there and return null, we still end up

accessible/base/nsAccessibilityService.h

@@ -153,6 +153,13 @@ class nsAccessibilityService final : public mozilla::a11y::DocManager,
   void GetStringRelationType(uint32_t aRelationType, nsAString& aString);
 
   // nsAccesibilityService
+  /**
+   * Notification used to update the accessible tree when deck panel is
+   * switched.
+   */
+  void DeckPanelSwitched(mozilla::PresShell* aPresShell, nsIContent* aDeckNode,
+                         nsIFrame* aPrevBoxFrame, nsIFrame* aCurrentBoxFrame);
+
   /**
    * Notification used to update the accessible tree when new content is
    * inserted.
@@ -233,10 +240,6 @@ class nsAccessibilityService final : public mozilla::a11y::DocManager,
   void NotifyOfComputedStyleChange(mozilla::PresShell* aPresShell,
                                    nsIContent* aContent);
 
-  void NotifyOfTabPanelVisibilityChange(mozilla::PresShell* aPresShell,
-                                        mozilla::dom::Element* aPanel,
-                                        bool aVisible);
-
   void NotifyOfResolutionChange(mozilla::PresShell* aPresShell,
                                 float aResolution);
 

accessible/generic/DocAccessible.cpp

@@ -14,6 +14,7 @@
 #include "nsAccCache.h"
 #include "nsAccessiblePivot.h"
 #include "nsAccUtils.h"
+#include "nsDeckFrame.h"
 #include "nsEventShell.h"
 #include "nsLayoutUtils.h"
 #include "nsTextEquivUtils.h"
@@ -1051,6 +1052,21 @@ LocalAccessible* DocAccessible::GetAccessibleOrContainer(
       return nullptr;
     }
 
+    // Check if node is in an unselected deck panel
+    if (aNoContainerIfPruned && currNode->IsXULElement()) {
+      if (nsIFrame* frame = currNode->AsContent()->GetPrimaryFrame()) {
+        nsDeckFrame* deckFrame = do_QueryFrame(frame->GetParent());
+        if (deckFrame && deckFrame->GetSelectedBox() != frame) {
+          // If deck is not a <tabpanels>, return null
+          nsIContent* parentFrameContent = deckFrame->GetContent();
+          if (!parentFrameContent ||
+              !parentFrameContent->IsXULElement(nsGkAtoms::tabpanels)) {
+            return nullptr;
+          }
+        }
+      }
+    }
+
     // Check if node is in zero-sized map
     if (aNoContainerIfPruned && currNode->IsHTMLElement(nsGkAtoms::map)) {
       if (nsIFrame* frame = currNode->AsContent()->GetPrimaryFrame()) {

accessible/generic/LocalAccessible.cpp

@@ -50,6 +50,7 @@
 #include "nsIContent.h"
 #include "nsIFormControl.h"
 
+#include "nsDeckFrame.h"
 #include "nsLayoutUtils.h"
 #include "nsPresContext.h"
 #include "nsIFrame.h"
@@ -69,7 +70,6 @@
 #include "nsArrayUtils.h"
 #include "nsWhitespaceTokenizer.h"
 #include "nsAttrName.h"
-#include "nsContainerFrame.h"
 
 #include "mozilla/Assertions.h"
 #include "mozilla/BasicEvents.h"
@@ -324,16 +324,22 @@ uint64_t LocalAccessible::VisibilityState() const {
       return states::INVISIBLE;
     }
 
-    if (nsLayoutUtils::IsPopup(curFrame)) {
-      return 0;
-    }
+    if (nsLayoutUtils::IsPopup(curFrame)) return 0;
 
-    if (curFrame->StyleUIReset()->mMozSubtreeHiddenOnlyVisually) {
-      // Offscreen state for background tab content.
+    // Offscreen state for background tab content and invisible for not selected
+    // deck panel.
+    nsIFrame* parentFrame = curFrame->GetParent();
+    nsDeckFrame* deckFrame = do_QueryFrame(parentFrame);
+    if (deckFrame && deckFrame->GetSelectedBox() != curFrame) {
+      if (deckFrame->GetContent()->IsXULElement(nsGkAtoms::tabpanels)) {
         return states::OFFSCREEN;
       }
 
-    nsIFrame* parentFrame = curFrame->GetParent();
+      MOZ_ASSERT_UNREACHABLE(
+          "Children of not selected deck panel are not accessible.");
+      return states::INVISIBLE;
+    }
+
     // If contained by scrollable frame then check that at least 12 pixels
     // around the object is visible, otherwise the object is offscreen.
     nsIScrollableFrame* scrollableFrame = do_QueryFrame(parentFrame);

accessible/mac/mozActionElements.mm

@@ -13,6 +13,7 @@
 #include "XULTabAccessible.h"
 #include "HTMLFormControlAccessible.h"
 
+#include "nsDeckFrame.h"
 #include "nsObjCExceptions.h"
 
 using namespace mozilla::a11y;
@@ -125,17 +126,26 @@ enum CheckboxValue {
 @implementation mozPaneAccessible
 
 - (NSArray*)moxChildren {
-  // By default, all tab panels are exposed in the a11y tree
-  // even if the tab they represent isn't the active tab. To
-  // prevent VoiceOver from navigating background tab content,
-  // only expose the tab panel that is currently on screen.
-  for (mozAccessible* child in [super moxChildren]) {
-    if (!([child state] & states::OFFSCREEN)) {
-      return [NSArray arrayWithObject:GetObjectOrRepresentedView(child)];
+  if (!mGeckoAccessible->AsLocal()) return nil;
+
+  nsDeckFrame* deckFrame =
+      do_QueryFrame(mGeckoAccessible->AsLocal()->GetFrame());
+  nsIFrame* selectedFrame = deckFrame ? deckFrame->GetSelectedBox() : nullptr;
+
+  LocalAccessible* selectedAcc = nullptr;
+  if (selectedFrame) {
+    nsINode* node = selectedFrame->GetContent();
+    selectedAcc = mGeckoAccessible->AsLocal()->Document()->GetAccessible(node);
   }
+
+  if (selectedAcc) {
+    mozAccessible* curNative = GetNativeFromGeckoAccessible(selectedAcc);
+    if (curNative)
+      return
+          [NSArray arrayWithObjects:GetObjectOrRepresentedView(curNative), nil];
   }
-  MOZ_ASSERT_UNREACHABLE("We have no on screen tab content?");
-  return @[];
+
+  return nil;
 }
 
 @end

accessible/tests/mochitest/attributes/test_obj_css.xhtml

@@ -22,6 +22,7 @@
       // CSS display
       testCSSAttrs("display_mozbox");
       testCSSAttrs("display_mozinlinebox");
+      testCSSAttrs("display_mozdeck");
       testCSSAttrs("display_mozpopup");
 
       SimpleTest.finish();
@@ -49,6 +50,7 @@
 
   <vbox id="display_mozbox" style="display: -moz-box;" role="img"/>
   <vbox id="display_mozinlinebox" style="display: -moz-inline-box;" role="img"/>
+  <vbox id="display_mozdeck" style="display: -moz-deck;" role="img"/>
   <vbox id="display_mozpopup" style="display: -moz-popup;" role="img"/>
 
   </hbox>

browser/base/content/browser.js

@@ -2171,23 +2171,23 @@ var gBrowserInit = {
         return;
       }
 
+      if (gBrowser.selectedBrowser.isRemoteBrowser) {
         // If the initial browser is remote, in order to optimize for first paint,
         // we'll defer switching focus to that browser until it has painted.
-      // Otherwise use a regular promise to guarantee that mutationobserver
-      // microtasks that could affect focusability have run.
-      let promise = gBrowser.selectedBrowser.isRemoteBrowser
-        ? this._firstContentWindowPaintDeferred.promise
-        : Promise.resolve();
-
-      promise.then(() => {
-        // If focus didn't move while we were waiting, we're okay to move to
-        // the browser.
+        this._firstContentWindowPaintDeferred.promise.then(() => {
+          // If focus didn't move while we were waiting for first paint, we're okay
+          // to move to the browser.
           if (
             document.commandDispatcher.focusedElement == initiallyFocusedElement
           ) {
             gBrowser.selectedBrowser.focus();
           }
         });
+      } else {
+        // If the initial browser is not remote, we can focus the browser
+        // immediately with no paint performance impact.
+        gBrowser.selectedBrowser.focus();
+      }
     });
 
     // Delay removing the attribute using requestAnimationFrame to avoid

browser/base/content/test/general/browser_bug495058.js

@@ -47,7 +47,7 @@ add_task(async function() {
     Assert.equal(
       win.document.activeElement,
       expectedActiveElement,
-      `${uri}: the active element is expected: ${win.document.activeElement?.nodeName}`
+      uri + ": the active element is expected"
     );
     Assert.equal(win.gURLBar.value, "", uri + ": urlbar is empty");
     Assert.ok(win.gURLBar.placeholder, uri + ": placeholder text is present");

browser/components/customizableui/test/browser_synced_tabs_menu.js

@@ -254,7 +254,11 @@ add_task(async function() {
 
   // The widget is still fetching tabs, as we've neutered everything that
   // provides them
-  is(deck.selectedIndex, DECKINDEX_FETCHING, "first deck entry is visible");
+  is(
+    deck.selectedIndex,
+    "" + DECKINDEX_FETCHING,
+    "first deck entry is visible"
+  );
 
   // Tell the widget there are tabs available, but with zero clients.
   mockedInternal.getTabClients = () => {
@@ -265,7 +269,7 @@ add_task(async function() {
   // The UI should be showing the "no clients" pane.
   is(
     deck.selectedIndex,
-    DECKINDEX_NOCLIENTS,
+    "" + DECKINDEX_NOCLIENTS,
     "no-clients deck entry is visible"
   );
 
@@ -316,7 +320,11 @@ add_task(async function() {
   await updateTabsPanel();
 
   // The UI should be showing tabs!
-  is(deck.selectedIndex, DECKINDEX_TABS, "no-clients deck entry is visible");
+  is(
+    deck.selectedIndex,
+    "" + DECKINDEX_TABS,
+    "no-clients deck entry is visible"
+  );
   let tabList = document.getElementById("PanelUI-remotetabs-tabslist");
   let node = tabList.firstElementChild;
   // First entry should be the client with the most-recent tab.
@@ -459,7 +467,7 @@ add_task(async function() {
   let subpanel = document.getElementById("PanelUI-remotetabs-main");
   ok(!subpanel.hidden, "main pane is visible");
   let deck = document.getElementById("PanelUI-remotetabs-deck");
-  is(deck.selectedIndex, DECKINDEX_TABS, "we should be showing tabs");
+  is(deck.selectedIndex, "" + DECKINDEX_TABS, "we should be showing tabs");
 
   function checkTabsPage(tabsShownCount, showMoreLabel) {
     let tabList = document.getElementById("PanelUI-remotetabs-tabslist");

browser/components/preferences/tests/browser_search_within_preferences_2.js

@@ -25,7 +25,7 @@ add_task(async function() {
   );
   is(
     weavePrefsDeck.selectedIndex,
-    0,
+    "0",
     "Should select the #noFxaAccount child node"
   );
 

browser/components/translation/test/browser_translation_infobar.js

@@ -103,7 +103,7 @@ add_task(async function test_infobar() {
   let notif = showTranslationUI("fr");
   is(
     notif.state,
-    Translation.STATE_OFFER,
+    "" + Translation.STATE_OFFER,
     "the infobar is offering translation"
   );
   is(
@@ -117,7 +117,7 @@ add_task(async function test_infobar() {
   notif._getAnonElt("translate").click();
   is(
     notif.state,
-    Translation.STATE_TRANSLATING,
+    "" + Translation.STATE_TRANSLATING,
     "the infobar is in the translating state"
   );
   ok(
@@ -134,14 +134,14 @@ add_task(async function test_infobar() {
 
   info("Make the translation fail and check we are in the error state.");
   notif.translation.failTranslation();
-  is(notif.state, Translation.STATE_ERROR, "infobar in the error state");
+  is(notif.state, "" + Translation.STATE_ERROR, "infobar in the error state");
   checkURLBarIcon();
 
   info("Click the try again button");
   notif._getAnonElt("tryAgain").click();
   is(
     notif.state,
-    Translation.STATE_TRANSLATING,
+    "" + Translation.STATE_TRANSLATING,
     "infobar in the translating state"
   );
   ok(
@@ -162,7 +162,7 @@ add_task(async function test_infobar() {
   notif.translation.finishTranslation();
   is(
     notif.state,
-    Translation.STATE_TRANSLATED,
+    "" + Translation.STATE_TRANSLATED,
     "infobar in the translated state"
   );
   checkURLBarIcon(true);
@@ -207,7 +207,7 @@ add_task(async function test_infobar() {
   from.doCommand();
   is(
     notif.state,
-    Translation.STATE_TRANSLATING,
+    "" + Translation.STATE_TRANSLATING,
     "infobar in the translating state"
   );
   ok(
@@ -232,7 +232,7 @@ add_task(async function test_infobar() {
   to.doCommand();
   is(
     notif.state,
-    Translation.STATE_TRANSLATING,
+    "" + Translation.STATE_TRANSLATING,
     "infobar in the translating state"
   );
   ok(
@@ -254,7 +254,7 @@ add_task(async function test_infobar() {
   notif = showTranslationUI("fr");
   is(
     notif.state,
-    Translation.STATE_OFFER,
+    "" + Translation.STATE_OFFER,
     "the infobar is offering translation"
   );
   is(
@@ -267,7 +267,7 @@ add_task(async function test_infobar() {
   notif._getAnonElt("translate").click();
   is(
     notif.state,
-    Translation.STATE_TRANSLATING,
+    "" + Translation.STATE_TRANSLATING,
     "the infobar is in the translating state"
   );
   ok(
@@ -332,7 +332,7 @@ add_task(async function test_infobar_using_page() {
   let notif = notificationBox.getNotificationWithValue("translation");
   is(
     notif.state,
-    Translation.STATE_OFFER,
+    "" + Translation.STATE_OFFER,
     "the infobar is offering translation"
   );
   is(

browser/modules/AsyncTabSwitcher.jsm

@@ -468,7 +468,7 @@ class AsyncTabSwitcher {
       let index = Array.prototype.indexOf.call(tabpanels.children, showPanel);
       if (index != -1) {
         this.log(`Switch to tab ${index} - ${this.tinfo(showTab)}`);
-        tabpanels.updateSelectedIndex(index);
+        tabpanels.setAttribute("selectedIndex", index);
         if (showTab === this.requestedTab) {
           if (requestedTabState == this.STATE_LOADED) {
             // The new tab will be made visible in the next paint, record the expected

browser/themes/osx/browser.css

@@ -397,11 +397,9 @@ moz-input-box > menupopup .context-menu-add-engine > .menu-iconic-left {
 }
 
 #tabbrowser-tabs {
-  /* overriding tabbox.css */
   -moz-box-align: stretch;
   margin-bottom: 0;
   position: static;
-  z-index: auto;
 }
 
 /* Bookmark drag and drop styles */

devtools/server/actors/animation-type-longhand.js

@@ -113,7 +113,6 @@ exports.ANIMATION_TYPE_FOR_LONGHANDS = [
       "object-fit",
       "-moz-orient",
       "-moz-osx-font-smoothing",
-      "-moz-subtree-hidden-only-visually",
       "outline-style",
       "overflow-anchor",
       "overflow-block",

layout/base/DisplayPortUtils.cpp

@@ -10,14 +10,18 @@
 #include "Layers.h"
 #include "mozilla/dom/BrowserChild.h"
 #include "mozilla/dom/Document.h"
+#include "mozilla/gfx/gfxVars.h"
 #include "mozilla/gfx/Point.h"
+#include "mozilla/layers/APZCCallbackHelper.h"
 #include "mozilla/layers/APZPublicUtils.h"
 #include "mozilla/layers/CompositorBridgeChild.h"
 #include "mozilla/layers/LayersMessageUtils.h"
 #include "mozilla/layers/PAPZ.h"
+#include "mozilla/layers/RepaintRequest.h"
 #include "mozilla/PresShell.h"
 #include "mozilla/StaticPrefs_layers.h"
 #include "mozilla/StaticPrefs_layout.h"
+#include "nsDeckFrame.h"
 #include "nsIScrollableFrame.h"
 #include "nsLayoutUtils.h"
 #include "nsPlaceholderFrame.h"
@@ -29,9 +33,13 @@
 
 namespace mozilla {
 
+using gfx::gfxVars;
 using gfx::IntSize;
 
+using layers::APZCCallbackHelper;
 using layers::FrameMetrics;
+using layers::LayerManager;
+using layers::RepaintRequest;
 using layers::ScrollableLayerGuid;
 
 typedef ScrollableLayerGuid::ViewID ViewID;
@@ -797,11 +805,12 @@ bool DisplayPortUtils::CalculateAndSetDisplayPortMargins(
                                aRepaintMode);
 }
 
-bool DisplayPortUtils::MaybeCreateDisplayPort(
-    nsDisplayListBuilder* aBuilder, nsIFrame* aScrollFrame,
-    nsIScrollableFrame* aScrollFrameAsScrollable, RepaintMode aRepaintMode) {
+bool DisplayPortUtils::MaybeCreateDisplayPort(nsDisplayListBuilder* aBuilder,
+                                              nsIFrame* aScrollFrame,
+                                              RepaintMode aRepaintMode) {
   nsIContent* content = aScrollFrame->GetContent();
-  if (!content) {
+  nsIScrollableFrame* scrollableFrame = do_QueryFrame(aScrollFrame);
+  if (!content || !scrollableFrame) {
     return false;
   }
 
@@ -814,7 +823,7 @@ bool DisplayPortUtils::MaybeCreateDisplayPort(
   if (aBuilder->IsPaintingToWindow() &&
       nsLayoutUtils::AsyncPanZoomEnabled(aScrollFrame) &&
       !aBuilder->HaveScrollableDisplayPort() &&
-      aScrollFrameAsScrollable->WantAsyncScroll()) {
+      scrollableFrame->WantAsyncScroll()) {
     // If we don't already have a displayport, calculate and set one.
     if (!haveDisplayPort) {
       // We only use the viewId for logging purposes, but create it
@@ -826,7 +835,7 @@ bool DisplayPortUtils::MaybeCreateDisplayPort(
           sDisplayportLog, LogLevel::Debug,
           ("Setting DP on first-encountered scrollId=%" PRIu64 "\n", viewId));
 
-      CalculateAndSetDisplayPortMargins(aScrollFrameAsScrollable, aRepaintMode);
+      CalculateAndSetDisplayPortMargins(scrollableFrame, aRepaintMode);
 #ifdef DEBUG
       haveDisplayPort = HasNonMinimalDisplayPort(content);
       MOZ_ASSERT(haveDisplayPort,
@@ -875,8 +884,10 @@ bool DisplayPortUtils::MaybeCreateDisplayPortInFirstScrollFrameEncountered(
       aFrame->GetContent()->GetID() == nsGkAtoms::tabbrowser_arrowscrollbox) {
     return false;
   }
-  if (nsIScrollableFrame* sf = do_QueryFrame(aFrame)) {
-    if (MaybeCreateDisplayPort(aBuilder, aFrame, sf, RepaintMode::Repaint)) {
+
+  nsIScrollableFrame* sf = do_QueryFrame(aFrame);
+  if (sf) {
+    if (MaybeCreateDisplayPort(aBuilder, aFrame, RepaintMode::Repaint)) {
       return true;
     }
   }
@@ -890,21 +901,28 @@ bool DisplayPortUtils::MaybeCreateDisplayPortInFirstScrollFrameEncountered(
   if (aFrame->IsSubDocumentFrame()) {
     PresShell* presShell = static_cast<nsSubDocumentFrame*>(aFrame)
                                ->GetSubdocumentPresShellForPainting(0);
-    if (nsIFrame* root = presShell ? presShell->GetRootFrame() : nullptr) {
+    nsIFrame* root = presShell ? presShell->GetRootFrame() : nullptr;
+    if (root) {
       if (MaybeCreateDisplayPortInFirstScrollFrameEncountered(root, aBuilder)) {
         return true;
       }
     }
   }
-  if (aFrame->StyleUIReset()->mMozSubtreeHiddenOnlyVisually) {
-    // Only descend the visible card of deck / tabpanels
-    return false;
+  if (aFrame->IsDeckFrame()) {
+    // only descend the visible card of a decks
+    nsIFrame* child = static_cast<nsDeckFrame*>(aFrame)->GetSelectedBox();
+    if (child) {
+      return MaybeCreateDisplayPortInFirstScrollFrameEncountered(child,
+                                                                 aBuilder);
     }
+  }
+
   for (nsIFrame* child : aFrame->PrincipalChildList()) {
     if (MaybeCreateDisplayPortInFirstScrollFrameEncountered(child, aBuilder)) {
       return true;
     }
   }
+
   return false;
 }
 

layout/base/DisplayPortUtils.h

@@ -278,9 +278,9 @@ class DisplayPortUtils {
    * Returns true if there is a displayport on an async scrollable scrollframe
    * after this call, either because one was just added or it already existed.
    */
-  static bool MaybeCreateDisplayPort(
-      nsDisplayListBuilder* aBuilder, nsIFrame* aScrollFrame,
-      nsIScrollableFrame* aScrollFrameAsScrollable, RepaintMode aRepaintMode);
+  static bool MaybeCreateDisplayPort(nsDisplayListBuilder* aBuilder,
+                                     nsIFrame* aScrollFrame,
+                                     RepaintMode aRepaintMode);
 
   /**
    * Sets a zero margin display port on all proper ancestors of aFrame that

layout/base/PresShell.cpp

@@ -3961,24 +3961,38 @@ void PresShell::ClearMouseCaptureOnView(nsView* aView) {
 }
 
 void PresShell::ClearMouseCapture() {
+  nsIContent* capturingContent = GetCapturingContent();
+  if (!capturingContent) {
+    AllowMouseCapture(false);
+    return;
+  }
+
   ReleaseCapturingContent();
   AllowMouseCapture(false);
 }
 
 void PresShell::ClearMouseCapture(nsIFrame* aFrame) {
-  MOZ_ASSERT(aFrame);
+  MOZ_ASSERT(
+      aFrame && aFrame->GetParent() &&
+          aFrame->GetParent()->Type() == LayoutFrameType::Deck,
+      "This function should only be called with a child frame of <deck>");
 
   nsIContent* capturingContent = GetCapturingContent();
   if (!capturingContent) {
+    AllowMouseCapture(false);
     return;
   }
 
   nsIFrame* capturingFrame = capturingContent->GetPrimaryFrame();
-  const bool shouldClear =
-      !capturingFrame ||
-      nsLayoutUtils::IsAncestorFrameCrossDocInProcess(aFrame, capturingFrame);
-  if (shouldClear) {
-    ClearMouseCapture();
+  if (!capturingFrame) {
+    ReleaseCapturingContent();
+    AllowMouseCapture(false);
+    return;
+  }
+
+  if (nsLayoutUtils::IsAncestorFrameCrossDocInProcess(aFrame, capturingFrame)) {
+    ReleaseCapturingContent();
+    AllowMouseCapture(false);
   }
 }
 

layout/base/PresShell.h

@@ -205,22 +205,13 @@ class PresShell final : public nsStubDocumentObserver,
 
   static void ClearMouseCaptureOnView(nsView* aView);
 
-  // Clear the capture content if it exists in this process.
-  static void ClearMouseCapture();
-
   // If a frame in the subtree rooted at aFrame is capturing the mouse then
   // clears that capture.
-  //
-  // NOTE(emilio): This is needed only so that mouse events captured by a remote
-  // frame don't remain being captured by the frame while hidden, see
-  // dom/events/test/browser_mouse_enterleave_switch_tab.js, which is the only
-  // test that meaningfully exercises this code path.
-  //
-  // We could consider maybe removing this, since the capturing content gets
-  // reset on mouse/pointerdown? Or maybe exposing an API so that the front-end
-  // does this.
   static void ClearMouseCapture(nsIFrame* aFrame);
 
+  // Clear the capture content if it exists in this process.
+  static void ClearMouseCapture();
+
 #ifdef ACCESSIBILITY
   /**
    * Return the document accessible for this PresShell if there is one.

layout/base/RestyleManager.cpp

@@ -2624,7 +2624,7 @@ MOZ_MAKE_ENUM_CLASS_BITWISE_OPERATORS(ServoPostTraversalFlags)
 // flags for kids.
 static ServoPostTraversalFlags SendA11yNotifications(
     nsPresContext* aPresContext, Element* aElement,
-    const ComputedStyle& aOldStyle, const ComputedStyle& aNewStyle,
+    ComputedStyle* aOldComputedStyle, ComputedStyle* aNewComputedStyle,
     ServoPostTraversalFlags aFlags) {
   using Flags = ServoPostTraversalFlags;
   MOZ_ASSERT(!(aFlags & Flags::SkipA11yNotifications) ||
@@ -2638,24 +2638,13 @@ static ServoPostTraversalFlags SendA11yNotifications(
     // enabled. Just skip everything.
     return Flags::Empty;
   }
-
-  if (aNewStyle.StyleUIReset()->mMozSubtreeHiddenOnlyVisually !=
-      aOldStyle.StyleUIReset()->mMozSubtreeHiddenOnlyVisually) {
-    if (aElement->GetParent() &&
-        aElement->GetParent()->IsXULElement(nsGkAtoms::tabpanels)) {
-      accService->NotifyOfTabPanelVisibilityChange(
-          aPresContext->PresShell(), aElement,
-          aNewStyle.StyleUIReset()->mMozSubtreeHiddenOnlyVisually);
-    }
-  }
-
   if (aFlags & Flags::SkipA11yNotifications) {
-    // Propagate the skipping flag to descendants.
+    // Propogate the skipping flag to descendants.
     return Flags::SkipA11yNotifications;
   }
 
   bool needsNotify = false;
-  bool isVisible = aNewStyle.StyleVisibility()->IsVisible();
+  bool isVisible = aNewComputedStyle->StyleVisibility()->IsVisible();
   if (aFlags & Flags::SendA11yNotificationsIfShown) {
     if (!isVisible) {
       // Propagate the sending-if-shown flag to descendants.
@@ -2668,7 +2657,7 @@ static ServoPostTraversalFlags SendA11yNotifications(
   } else {
     // If we shouldn't skip in any case, we need to check whether our
     // own visibility has changed.
-    bool wasVisible = aOldStyle.StyleVisibility()->IsVisible();
+    bool wasVisible = aOldComputedStyle->StyleVisibility()->IsVisible();
     needsNotify = wasVisible != isVisible;
   }
 
@@ -2898,9 +2887,9 @@ bool RestyleManager::ProcessPostTraversal(Element* aElement,
     AddLayerChangesForAnimation(styleFrame, primaryFrame, aElement, changeHint,
                                 aRestyleState.ChangeList());
 
-    childrenFlags |= SendA11yNotifications(mPresContext, aElement,
-                                           *oldOrDisplayContentsStyle,
-                                           *upToDateStyle, aFlags);
+    childrenFlags |=
+        SendA11yNotifications(mPresContext, aElement, oldOrDisplayContentsStyle,
+                              upToDateStyle, aFlags);
   }
 
   const bool traverseElementChildren =

layout/base/crashtests/344300-2.html

@@ -0,0 +1,10 @@
+<html><body>
+<object style="display:-moz-deck;">
+<noscript>
+</noscript>
+</object>
+</body></html>
+
+
+
+

layout/base/crashtests/373628.html

@@ -58,13 +58,16 @@ window.location.reload();
 <s style=" display: -moz-box; position: absolute; direction: ltr;">
 <q style=" display: table; direction: ltr;">
 <bdo style=" display: block;">mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m 
+<q style=" display: -moz-deck; position: absolute; direction: rtl;">mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m 
+</q>
 </bdo>
 </q>
 </s>
 <map style=" display: inline-table; position: fixed; direction: ltr;">
 <q style=" display: table; direction: ltr;">
 <bdo style=" display: block;">
-mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m 
+<q style=" display: -moz-deck; position: absolute; direction: rtl;">mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m 
+</q>mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m 
 <q style=" display: inline;  direction: ltr;">mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m 
 </q>
 </bdo>
@@ -363,6 +366,7 @@ mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m
 </q>
 </q>
 </q>
+<listing style=" display: -moz-deck; direction: ltr;">
 <p style=" display: block; position: fixed; direction: ltr;">
 <q style=" display: table-header-group; ">
 <q style=" display: table-cell; ">
@@ -401,6 +405,7 @@ mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m
 </q>
 </q>
 </p>
+</listing>
 <q style=" display: table-header-group; ">
 <q style=" display: table-cell; ">
 <q style=" display: table; direction: ltr;">
@@ -651,7 +656,7 @@ mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m
 </map>
 <ol style="display: inline-block;direction: ltr;">
 <p style="display: inherit;position: fixed;direction: ltr;">
-<body style="display: position: absolute;direction: ltr;">mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m 
+<body style="display: -moz-deck;position: absolute;direction: ltr;">mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m 
 </ol>mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m 
 </html>mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m 
 </map>mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m mm m 

layout/base/crashtests/570038-1.html

@@ -0,0 +1,4 @@
+<!DOCTYPE html>
+<html>
+<body><div style="display: -moz-deck;"><div style="overflow: auto; border: 4294967296px solid blue;">M</div></div></body>
+</html>

layout/base/crashtests/crashtests.list

@@ -105,6 +105,7 @@ load 343540-1.html
 load 344057-1.xhtml
 load 344064-1.html
 load 344300-1.html
+load 344300-2.html
 load chrome://reftest/content/crashtests/layout/base/crashtests/344340-1.xhtml
 load 347898-1.html
 load 348126-1.html
@@ -315,6 +316,7 @@ load 543648-1.html
 load 560447-1.html
 load 564063-1.html
 load 569018-1.html
+load chrome://reftest/content/crashtests/layout/base/crashtests/570038-1.html
 load chrome://reftest/content/crashtests/layout/base/crashtests/572003.xhtml
 load 572582-1.xhtml
 load 576649-1.html

layout/base/nsCSSFrameConstructor.cpp

@@ -215,6 +215,8 @@ nsContainerFrame* NS_NewRootBoxFrame(PresShell* aPresShell,
 nsContainerFrame* NS_NewDocElementBoxFrame(PresShell* aPresShell,
                                            ComputedStyle* aStyle);
 
+nsIFrame* NS_NewDeckFrame(PresShell* aPresShell, ComputedStyle* aStyle);
+
 nsIFrame* NS_NewLeafBoxFrame(PresShell* aPresShell, ComputedStyle* aStyle);
 
 nsIFrame* NS_NewRangeFrame(PresShell* aPresShell, ComputedStyle* aStyle);
@@ -4547,6 +4549,11 @@ nsCSSFrameConstructor::FindDisplayData(const nsStyleDisplay& aDisplay,
           FCDATA_DESIRED_PARENT_TYPE_TO_BITS(eTypeRuby));
       return &data;
     }
+    case StyleDisplayInside::MozDeck: {
+      static constexpr FrameConstructionData data =
+          SIMPLE_XUL_FCDATA(NS_NewDeckFrame);
+      return &data;
+    }
     case StyleDisplayInside::MozPopup: {
       static constexpr FrameConstructionData data(
           NS_NewMenuPopupFrame, FCDATA_DISALLOW_OUT_OF_FLOW | FCDATA_IS_POPUP |

layout/base/nsLayoutUtils.cpp

@@ -117,6 +117,7 @@
 #include "nsCSSPseudoElements.h"
 #include "nsCSSRendering.h"
 #include "nsTHashMap.h"
+#include "nsDeckFrame.h"
 #include "nsDisplayList.h"
 #include "nsFlexContainerFrame.h"
 #include "nsFontInflationData.h"

layout/build/nsLayoutStatics.cpp

@@ -35,6 +35,7 @@
 #include "nsRepeatService.h"
 #include "nsFloatManager.h"
 #include "nsSprocketLayout.h"
+#include "nsStackLayout.h"
 #include "nsTextControlFrame.h"
 #include "txMozillaXSLTProcessor.h"
 #include "nsTreeSanitizer.h"
@@ -328,6 +329,7 @@ void nsLayoutStatics::Shutdown() {
   nsColorNames::ReleaseTable();
   nsCSSProps::ReleaseTable();
   nsRepeatService::Shutdown();
+  nsStackLayout::Shutdown();
 
   nsXULContentUtils::Finish();
   nsXULPrototypeCache::ReleaseGlobals();

layout/forms/crashtests/378413-1.xhtml

@@ -0,0 +1,16 @@
+<html xmlns="http://www.w3.org/1999/xhtml">
+<body style="direction: rtl;">
+
+<form style="display: -moz-deck; width: 1em;">
+<fieldset>
+  <legend>Your name</legend>
+  <input type="text" name="name" size="20"/>
+</fieldset>
+<fieldset>
+  <legend>Your E-mail address</legend>
+  <input type="text" name="email" size="25"/>
+</fieldset>
+</form>
+
+</body>
+</html>

layout/forms/crashtests/crashtests.list

@@ -20,6 +20,7 @@ load 370703-1.html
 load 370940-1.html
 load 370967.html
 load 378369.html
+load 378413-1.xhtml
 load 380116-1.xhtml
 load 382610-1.html
 load 383887-1.html

layout/generic/FrameClasses.py

@@ -22,6 +22,7 @@ FRAME_CLASSES = [
     Frame("nsComboboxDisplayFrame", "ComboboxDisplay", NOT_LEAF),
     Frame("nsContinuingTextFrame", "Text", LEAF),
     Frame("nsDateTimeControlFrame", "DateTimeControl", NOT_LEAF),
+    Frame("nsDeckFrame", "Deck", NOT_LEAF),
     Frame("nsDocElementBoxFrame", "DocElementBox", NOT_LEAF),
     Frame("nsFieldSetFrame", "FieldSet", NOT_LEAF),
     Frame("nsFileControlFrame", "Block", LEAF),

layout/generic/crashtests/370866-1.xhtml

@@ -0,0 +1,14 @@
+<html xmlns="http://www.w3.org/1999/xhtml">
+
+<head>
+</head>
+
+<body>
+
+<table style="display: -moz-deck;"><tbody><tr><td>
+  <span style="position: relative;"><marquee><marquee><span style="position: absolute;">X</span></marquee></marquee></span>
+</td></tr></tbody></table>
+
+</body>
+
+</html>

layout/generic/crashtests/381786-1.html

@@ -0,0 +1,17 @@
+<!DOCTYPE html>
+<html>
+<body>
+
+<div style="display:-moz-deck">
+  <div>
+    <span style="float: right; width: 0;">x</span>
+  </div>
+  <div style="position: relative;">
+    <span style="float: right;">
+      <span style="position: absolute;">y</span>
+    </span>
+  </div>
+</div>
+
+</body>
+</html>

layout/generic/crashtests/862947-1.html

@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+<html>
+<head>
+<style>
+
+div { display: flex; }
+div:after { display: -moz-deck; content: counter(b); }
+
+</style>
+</head>
+<body>
+
+<div></div>
+
+</body>
+</html>

layout/generic/crashtests/crashtests.list

@@ -87,6 +87,7 @@ load 370174-2.html
 load 370174-3.html
 load 370699-1.html
 load 370794-1.html
+load 370866-1.xhtml
 load 370884-1.xhtml
 load 371348-1.xhtml
 load 371561-1.html
@@ -103,6 +104,7 @@ load 379217-2.xhtml
 load 379917-1.xhtml
 load 380012-1.html
 load 381152-1.html
+load 381786-1.html
 load 382129-1.xhtml
 load 382131-1.html
 load 382199-1.html
@@ -534,6 +536,7 @@ asserts(8-46) load 850931.html # nested multicols, inner multicol has column-wid
 load 851396-1.html
 load 854263-1.html
 load 862185.html
+load 862947-1.html
 load 863935.html
 load 866547-1.html
 needs-focus pref(accessibility.browsewithcaret,true) load 868906.html

layout/generic/nsIFrame.cpp

@@ -100,6 +100,7 @@
 #include "nsBlockFrame.h"
 #include "nsDisplayList.h"
 #include "nsChangeHint.h"
+#include "nsDeckFrame.h"
 #include "nsSubDocumentFrame.h"
 #include "RetainedDisplayListBuilder.h"
 
@@ -374,19 +375,17 @@ bool nsIFrame::IsVisibleConsideringAncestors(uint32_t aFlags) const {
   const nsIFrame* frame = this;
   while (frame) {
     nsView* view = frame->GetView();
-    if (view && view->GetVisibility() == nsViewVisibility_kHide) {
-      return false;
+    if (view && view->GetVisibility() == nsViewVisibility_kHide) return false;
+
+    if (this != frame && frame->HidesContent()) return false;
+
+    nsIFrame* parent = frame->GetParent();
+    nsDeckFrame* deck = do_QueryFrame(parent);
+    if (deck) {
+      if (deck->GetSelectedBox() != frame) return false;
     }
 
-    if (frame->StyleUIReset()->mMozSubtreeHiddenOnlyVisually) {
-      return false;
-    }
-
-    if (this != frame && frame->HidesContent()) {
-      return false;
-    }
-
-    if (nsIFrame* parent = frame->GetParent()) {
+    if (parent) {
       frame = parent;
     } else {
       parent = nsLayoutUtils::GetCrossDocParentFrameInProcess(frame);
@@ -1287,10 +1286,6 @@ void nsIFrame::DidSetComputedStyle(ComputedStyle* aOldComputedStyle) {
         scrollableFrame->PostPendingResnap();
       }
     }
-    if (StyleUIReset()->mMozSubtreeHiddenOnlyVisually &&
-        !aOldComputedStyle->StyleUIReset()->mMozSubtreeHiddenOnlyVisually) {
-      PresShell::ClearMouseCapture(this);
-    }
   } else {  // !aOldComputedStyle
     handleStickyChange = disp->mPosition == StylePositionProperty::Sticky;
   }
@@ -3988,21 +3983,22 @@ static bool ShouldSkipFrame(nsDisplayListBuilder* aBuilder,
   if (aBuilder->IsBackgroundOnly()) {
     return true;
   }
+
   if (aBuilder->IsForGenerateGlyphMask() &&
       (!aFrame->IsTextFrame() && aFrame->IsLeaf())) {
     return true;
   }
+
   // The placeholder frame should have the same content as the OOF frame.
   if (aBuilder->GetSelectedFramesOnly() &&
       (aFrame->IsLeaf() && !aFrame->IsSelected())) {
     return true;
   }
+
   static const nsFrameState skipFlags =
       (NS_FRAME_TOO_DEEP_IN_FRAME_TREE | NS_FRAME_IS_NONDISPLAY);
-  if (aFrame->HasAnyStateBits(skipFlags)) {
-    return true;
-  }
-  return aFrame->StyleUIReset()->mMozSubtreeHiddenOnlyVisually;
+
+  return aFrame->HasAnyStateBits(skipFlags);
 }
 
 void nsIFrame::BuildDisplayListForChild(nsDisplayListBuilder* aBuilder,

layout/reftests/bugs/411367-3-ref.html

@@ -0,0 +1,8 @@
+<!DOCTYPE html>
+<html>
+<head>
+</head>
+<body>
+<div style="display: -moz-deck;" id="s">x</div>
+</body>
+</html>

layout/reftests/bugs/411367-3.html

@@ -0,0 +1,8 @@
+<!DOCTYPE html>
+<html>
+<head>
+</head>
+<body onload="document.getElementById('s').firstChild.data = 'x';">
+<div style="display: -moz-deck;" id="s"> </div>
+</body>
+</html>

layout/reftests/bugs/reftest.list

@@ -926,6 +926,7 @@ fuzzy-if(winWidget,0-123,0-1900) fuzzy-if(swgl,0-1,0-39) == 409659-1d.html 40965
 == 410621-1.html 410621-1-ref.html
 == 411059-1.html 411059-1-ref.html
 fuzzy-if(winWidget,46-129,652-770) == 411334-1.xml 411334-1-ref.xml
+== 411367-3.html 411367-3-ref.html
 == 411585-1.html 411585-1-ref.html
 == 411585-2.html 411585-2-ref.html
 fails == 411585-3.html 411585-3-ref.html # bug 426909

layout/style/ServoBindings.toml

@@ -607,7 +607,6 @@ cbindgen-types = [
     { gecko = "StyleFontStyle", servo = "crate::values::computed::font::FontStyle" },
     { gecko = "StyleFontWeight", servo = "crate::values::computed::font::FontWeight" },
     { gecko = "StyleFontStretch", servo = "crate::values::computed::font::FontStretch" },
-    { gecko = "StyleBoolInteger", servo = "crate::values::computed::BoolInteger" },
 ]
 
 mapped-generic-types = [

layout/style/nsStyleConsts.h

@@ -91,6 +91,8 @@ enum class StyleDisplay : uint16_t {
       StyleDisplayFrom(StyleDisplayOutside::Block, StyleDisplayInside::MozBox),
   MozInlineBox =
       StyleDisplayFrom(StyleDisplayOutside::Inline, StyleDisplayInside::MozBox),
+  MozDeck =
+      StyleDisplayFrom(StyleDisplayOutside::XUL, StyleDisplayInside::MozDeck),
   MozPopup =
       StyleDisplayFrom(StyleDisplayOutside::XUL, StyleDisplayInside::MozPopup),
 };

layout/style/nsStyleStruct.cpp

@@ -3213,8 +3213,7 @@ nsChangeHint nsStyleUI::CalcDifference(const nsStyleUI& aNewData) const {
 nsStyleUIReset::nsStyleUIReset(const Document& aDocument)
     : mUserSelect(StyleUserSelect::Auto),
       mScrollbarWidth(StyleScrollbarWidth::Auto),
-      mMozForceBrokenImageIcon(false),
-      mMozSubtreeHiddenOnlyVisually(false),
+      mMozForceBrokenImageIcon(0),
       mIMEMode(StyleImeMode::Auto),
       mWindowDragging(StyleWindowDragging::Default),
       mWindowShadow(StyleWindowShadow::Default),
@@ -3251,7 +3250,6 @@ nsStyleUIReset::nsStyleUIReset(const nsStyleUIReset& aSource)
     : mUserSelect(aSource.mUserSelect),
       mScrollbarWidth(aSource.mScrollbarWidth),
       mMozForceBrokenImageIcon(aSource.mMozForceBrokenImageIcon),
-      mMozSubtreeHiddenOnlyVisually(aSource.mMozSubtreeHiddenOnlyVisually),
       mIMEMode(aSource.mIMEMode),
       mWindowDragging(aSource.mWindowDragging),
       mWindowShadow(aSource.mWindowShadow),
@@ -3289,9 +3287,6 @@ nsChangeHint nsStyleUIReset::CalcDifference(
   if (mMozForceBrokenImageIcon != aNewData.mMozForceBrokenImageIcon) {
     hint |= nsChangeHint_ReconstructFrame;
   }
-  if (mMozSubtreeHiddenOnlyVisually != aNewData.mMozSubtreeHiddenOnlyVisually) {
-    hint |= nsChangeHint_RepaintFrame;
-  }
   if (mScrollbarWidth != aNewData.mScrollbarWidth) {
     // For scrollbar-width change, we need some special handling similar
     // to overflow properties. Specifically, we may need to reconstruct

layout/style/nsStyleStruct.h

@@ -1863,8 +1863,7 @@ struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleUIReset {
     return mAnimations[aIndex % mAnimationTimelineCount].GetTimeline();
   }
 
-  mozilla::StyleBoolInteger mMozForceBrokenImageIcon;
-  mozilla::StyleBoolInteger mMozSubtreeHiddenOnlyVisually;
+  uint8_t mMozForceBrokenImageIcon;  // (0 if not forcing, otherwise forcing)
   mozilla::StyleImeMode mIMEMode;
   mozilla::StyleWindowDragging mWindowDragging;
   mozilla::StyleWindowShadow mWindowShadow;

layout/style/test/ListCSSProperties.cpp

@@ -104,7 +104,6 @@ const char* gInaccessibleProperties[] = {
     "-moz-min-font-size-ratio",              // parsed by UA sheets only
     "-moz-box-layout",                       // chrome-only internal properties
     "-moz-font-smoothing-background-color",  // chrome-only internal properties
-    "-moz-subtree-hidden-only-visually",     // chrome-only internal properties
     "-moz-window-input-region-margin",       // chrome-only internal properties
     "-moz-window-opacity",                   // chrome-only internal properties
     "-moz-window-transform",                 // chrome-only internal properties

layout/style/test/mochitest.ini

@@ -134,6 +134,8 @@ skip-if = true # Bug 701060
 [test_bug418986-2.html]
 [test_bug437915.html]
 [test_bug450191.html]
+[test_bug453896_deck.html]
+support-files = bug453896_iframe.html
 [test_bug470769.html]
 [test_bug499655.html]
 [test_bug499655.xhtml]

layout/style/test/test_bug453896_deck.html

@@ -0,0 +1,42 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=453896
+-->
+<head>
+  <title>Test for Bug 453896</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body onload="run()">
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=453896">Mozilla Bug 453896</a>
+<div id="display">
+
+<div style="display:-moz-deck; height: 300px; width: 300px;">
+  <iframe src="about:blank"></iframe>
+  <iframe id="subdoc" src="bug453896_iframe.html"></iframe>
+  <iframe src="about:blank"></iframe>
+</div>
+
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+/** Test for Bug 453896 **/
+
+function run()
+{
+  var iframe = document.getElementById("subdoc");
+  var subdoc = iframe.contentDocument;
+  var subwin = iframe.contentWindow;
+
+  subwin.run(window);
+  SimpleTest.finish();
+}
+
+SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
+

layout/style/test/test_non_content_accessible_values.html

@@ -19,6 +19,7 @@ const NON_CONTENT_ACCESSIBLE_VALUES = {
     "-moz-autofill-background",
   ],
   "display": [
+    "-moz-deck",
     "-moz-popup",
     "-moz-box",
     "-moz-inline-box",

layout/xul/crashtests/290743.html

@@ -0,0 +1,6 @@
+<html>
+<head><title>Testcase bug 290743 - This display:-moz-deck testcase freezes Mozilla</title></head>
+<body style="display:-moz-deck;">
+<input type="radio"><input type="radio">
+</body>
+</html>

layout/xul/crashtests/311457-1.html

@@ -0,0 +1,12 @@
+<html><head>
+
+</head>
+
+<body>
+
+<div style="display: -moz-deck"><div style="display: -moz-popup"></div></div>
+
+<div style="position: relative">Y</div>
+
+</body>
+</html>

layout/xul/crashtests/374102-1.xhtml

@@ -0,0 +1,5 @@
+<window xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
+<tabpanels>
+<treechildren style="display: -moz-deck;"/>
+</tabpanels>
+</window>

layout/xul/crashtests/399013.xhtml

@@ -0,0 +1,31 @@
+<window xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
+<menulist id="b" style="display: -moz-box;">
+<panel id="c" style=" position: absolute;">
+<popup onunderflow="document.getElementById('c').removeAttribute('style')"/>
+</panel>
+<menupopup id="a" style="display: -moz-box;">
+<menulist/>
+</menupopup>
+<panel style="display: -moz-deck;" onoverflow="document.getElementById('b').removeAttribute('style')">
+<popup style="display: -moz-deck;"/>
+</panel>
+</menulist>
+
+<script id="script" xmlns="http://www.w3.org/1999/xhtml"><![CDATA[
+function doe() {
+document.getElementById('c').removeAttribute('style');
+document.documentElement.clientHeight;
+document.getElementById('b').removeAttribute('style');
+document.getElementById('a').setAttribute('selected', 'true');
+document.getElementById('a').setAttribute('style', 'position: fixed;');
+document.documentElement.clientHeight;
+document.getElementById('a').removeAttribute('style');
+}
+
+function doe2() {
+window.location.reload();
+}
+setTimeout(doe2, 200);
+setTimeout(doe,100);
+]]></script>
+</window>

layout/xul/crashtests/crashtests.list

@@ -5,10 +5,12 @@ load chrome://reftest/content/crashtests/layout/xul/crashtests/151826-1.xhtml
 load chrome://reftest/content/crashtests/layout/xul/crashtests/168724-1.xhtml
 load chrome://reftest/content/crashtests/layout/xul/crashtests/189814-1.xhtml
 skip-if(Android) load chrome://reftest/content/crashtests/layout/xul/crashtests/289410-1.xhtml
+load 290743.html
 load chrome://reftest/content/crashtests/layout/xul/crashtests/291702-1.xhtml
 load chrome://reftest/content/crashtests/layout/xul/crashtests/291702-2.xhtml
 load chrome://reftest/content/crashtests/layout/xul/crashtests/291702-3.xhtml
 load chrome://reftest/content/crashtests/layout/xul/crashtests/294371-1.xhtml
+load 311457-1.html
 load chrome://reftest/content/crashtests/layout/xul/crashtests/322786-1.xhtml
 skip-if(Android) load chrome://reftest/content/crashtests/layout/xul/crashtests/325377.xhtml
 skip-if(Android) load chrome://reftest/content/crashtests/layout/xul/crashtests/326879-1.xhtml
@@ -22,6 +24,7 @@ load chrome://reftest/content/crashtests/layout/xul/crashtests/366112-1.xhtml
 skip-if(Android) load chrome://reftest/content/crashtests/layout/xul/crashtests/366203-1.xhtml
 load 367185-1.xhtml
 load 369942-1.xhtml
+skip-if(Android) load chrome://reftest/content/crashtests/layout/xul/crashtests/374102-1.xhtml
 load 376137-1.html
 load 376137-2.html
 load 377592-1.svg
@@ -36,6 +39,7 @@ load 384871-1.html
 load chrome://reftest/content/crashtests/layout/xul/crashtests/386642.xhtml
 load chrome://reftest/content/crashtests/layout/xul/crashtests/387080-1.xhtml
 load 391974-1.html
+skip-if(Android) load chrome://reftest/content/crashtests/layout/xul/crashtests/399013.xhtml
 load 402912-1.xhtml
 load 404192.xhtml
 load chrome://reftest/content/crashtests/layout/xul/crashtests/408904-1.xhtml

layout/xul/moz.build

@@ -23,6 +23,7 @@ UNIFIED_SOURCES += [
     "nsBoxFrame.cpp",
     "nsBoxLayout.cpp",
     "nsBoxLayoutState.cpp",
+    "nsDeckFrame.cpp",
     "nsDocElementBoxFrame.cpp",
     "nsImageBoxFrame.cpp",
     "nsLeafBoxFrame.cpp",
@@ -38,6 +39,7 @@ UNIFIED_SOURCES += [
     "nsSliderFrame.cpp",
     "nsSplitterFrame.cpp",
     "nsSprocketLayout.cpp",
+    "nsStackLayout.cpp",
     "nsTextBoxFrame.cpp",
     "nsXULPopupManager.cpp",
     "nsXULTooltipListener.cpp",

layout/xul/nsBox.cpp

@@ -308,7 +308,8 @@ nsresult nsIFrame::SyncXULLayout(nsBoxLayoutState& aBoxLayoutState) {
 nsresult nsIFrame::XULRedraw(nsBoxLayoutState& aState) {
   if (aState.PaintingDisabled()) return NS_OK;
 
-  // Unclear whether we could get away with just InvalidateFrame().
+  // nsStackLayout, at least, expects us to repaint descendants even
+  // if a damage rect is provided
   InvalidateFrameSubtree();
 
   return NS_OK;

layout/xul/nsDeckFrame.cpp

@@ -0,0 +1,283 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//
+// Eric Vaughan
+// Netscape Communications
+//
+// See documentation in associated header file
+//
+
+#include "nsDeckFrame.h"
+#include "mozilla/ComputedStyle.h"
+#include "mozilla/PresShell.h"
+#include "nsLayoutUtils.h"
+#include "nsPresContext.h"
+#include "nsIContent.h"
+#include "nsCOMPtr.h"
+#include "nsNameSpaceManager.h"
+#include "nsGkAtoms.h"
+#include "nsHTMLParts.h"
+#include "nsCSSRendering.h"
+#include "nsViewManager.h"
+#include "nsBoxLayoutState.h"
+#include "nsStackLayout.h"
+#include "nsDisplayList.h"
+#include "nsContainerFrame.h"
+#include "nsContentUtils.h"
+#include "nsXULPopupManager.h"
+#include "nsImageBoxFrame.h"
+#include "nsImageFrame.h"
+
+#ifdef ACCESSIBILITY
+#  include "nsAccessibilityService.h"
+#endif
+
+using namespace mozilla;
+
+nsIFrame* NS_NewDeckFrame(PresShell* aPresShell, ComputedStyle* aStyle) {
+  return new (aPresShell) nsDeckFrame(aStyle, aPresShell->GetPresContext());
+}
+
+NS_IMPL_FRAMEARENA_HELPERS(nsDeckFrame)
+
+NS_QUERYFRAME_HEAD(nsDeckFrame)
+  NS_QUERYFRAME_ENTRY(nsDeckFrame)
+NS_QUERYFRAME_TAIL_INHERITING(nsBoxFrame)
+
+nsDeckFrame::nsDeckFrame(ComputedStyle* aStyle, nsPresContext* aPresContext)
+    : nsBoxFrame(aStyle, aPresContext, kClassID) {
+  nsCOMPtr<nsBoxLayout> layout;
+  NS_NewStackLayout(layout);
+  SetXULLayoutManager(layout);
+}
+
+nsresult nsDeckFrame::AttributeChanged(int32_t aNameSpaceID, nsAtom* aAttribute,
+                                       int32_t aModType) {
+  nsresult rv =
+      nsBoxFrame::AttributeChanged(aNameSpaceID, aAttribute, aModType);
+
+  // if the index changed hide the old element and make the new element visible
+  if (aAttribute == nsGkAtoms::selectedIndex) {
+    IndexChanged();
+  }
+
+  return rv;
+}
+
+void nsDeckFrame::Init(nsIContent* aContent, nsContainerFrame* aParent,
+                       nsIFrame* aPrevInFlow) {
+  nsBoxFrame::Init(aContent, aParent, aPrevInFlow);
+
+  mIndex = GetSelectedIndex();
+}
+
+void nsDeckFrame::ShowBox(nsIFrame* aBox) { Animate(aBox, true); }
+
+void nsDeckFrame::HideBox(nsIFrame* aBox) {
+  PresShell::ClearMouseCapture(aBox);
+  Animate(aBox, false);
+}
+
+void nsDeckFrame::IndexChanged() {
+  // did the index change?
+  int32_t index = GetSelectedIndex();
+
+  if (index == mIndex) return;
+
+  // redraw
+  InvalidateFrame();
+
+  // hide the currently showing box
+  nsIFrame* currentBox = GetSelectedBox();
+  if (currentBox)  // only hide if it exists
+    HideBox(currentBox);
+
+  mSelectedBoxCache = nullptr;
+
+  mIndex = index;
+
+  ShowBox(GetSelectedBox());
+
+#ifdef ACCESSIBILITY
+  nsAccessibilityService* accService = GetAccService();
+  if (accService) {
+    accService->DeckPanelSwitched(PresContext()->GetPresShell(), mContent,
+                                  currentBox, GetSelectedBox());
+  }
+#endif
+
+  // Force any popups that might be anchored on elements within hidden
+  // box to update.
+  nsXULPopupManager* pm = nsXULPopupManager::GetInstance();
+  if (pm && currentBox) {
+    pm->UpdatePopupPositions(currentBox->PresContext()->RefreshDriver());
+  }
+}
+
+int32_t nsDeckFrame::GetSelectedIndex() {
+  // default index is 0
+  int32_t index = 0;
+
+  // get the index attribute
+  nsAutoString value;
+  if (mContent->AsElement()->GetAttr(kNameSpaceID_None,
+                                     nsGkAtoms::selectedIndex, value)) {
+    nsresult error;
+
+    // convert it to an integer
+    index = value.ToInteger(&error);
+  }
+
+  return index;
+}
+
+nsIFrame* nsDeckFrame::GetSelectedBox() {
+  if (!mSelectedBoxCache && mIndex >= 0) {
+    mSelectedBoxCache = (mIndex >= 0) ? mFrames.FrameAt(mIndex) : nullptr;
+  }
+  return mSelectedBoxCache;
+}
+
+void nsDeckFrame::BuildDisplayList(nsDisplayListBuilder* aBuilder,
+                                   const nsDisplayListSet& aLists) {
+  // if a tab is hidden all its children are too.
+  if (StyleVisibility()->mVisible == StyleVisibility::Hidden) {
+    return;
+  }
+  nsBoxFrame::BuildDisplayList(aBuilder, aLists);
+}
+
+void nsDeckFrame::RemoveFrame(ChildListID aListID, nsIFrame* aOldFrame) {
+  nsIFrame* currentFrame = GetSelectedBox();
+  if (aOldFrame == currentFrame) {
+    mSelectedBoxCache = nullptr;
+  }
+
+  if (currentFrame && aOldFrame && currentFrame != aOldFrame) {
+    // If the frame we're removing is at an index that's less
+    // than mIndex, that means we're going to be shifting indexes
+    // by 1.
+    //
+    // We attempt to keep the same child displayed by automatically
+    // updating our internal notion of the current index.
+    int32_t removedIndex = mFrames.IndexOf(aOldFrame);
+    MOZ_ASSERT(removedIndex >= 0,
+               "A deck child was removed that was not in mFrames.");
+    if (removedIndex < mIndex) {
+      // This shouldn't invalidate our cache, but be really paranoid, it's not
+      // that important to keep our cache here.
+      mSelectedBoxCache = nullptr;
+
+      mIndex--;
+      // This is going to cause us to handle the index change in IndexedChanged,
+      // but since the new index will match mIndex, it's essentially a noop.
+      nsContentUtils::AddScriptRunner(new nsSetAttrRunnable(
+          mContent->AsElement(), nsGkAtoms::selectedIndex, mIndex));
+    }
+  }
+  nsBoxFrame::RemoveFrame(aListID, aOldFrame);
+}
+
+void nsDeckFrame::BuildDisplayListForChildren(nsDisplayListBuilder* aBuilder,
+                                              const nsDisplayListSet& aLists) {
+  // only paint the selected box
+  nsIFrame* box = GetSelectedBox();
+  if (!box) return;
+
+  // Putting the child in the background list. This is a little weird but
+  // it matches what we were doing before.
+  nsDisplayListSet set(aLists, aLists.BlockBorderBackgrounds());
+  BuildDisplayListForChild(aBuilder, box, set);
+}
+
+void nsDeckFrame::Animate(nsIFrame* aParentBox, bool start) {
+  if (!aParentBox) return;
+
+  nsImageBoxFrame* imgBoxFrame = do_QueryFrame(aParentBox);
+  nsImageFrame* imgFrame = do_QueryFrame(aParentBox);
+
+  if (imgBoxFrame) {
+    if (start)
+      imgBoxFrame->RestartAnimation();
+    else
+      imgBoxFrame->StopAnimation();
+  }
+
+  if (imgFrame) {
+    if (start)
+      imgFrame->RestartAnimation();
+    else
+      imgFrame->StopAnimation();
+  }
+
+  for (const auto& childList : aParentBox->ChildLists()) {
+    for (nsIFrame* child : childList.mList) {
+      Animate(child, start);
+    }
+  }
+}
+
+NS_IMETHODIMP
+nsDeckFrame::DoXULLayout(nsBoxLayoutState& aState) {
+  // Make sure we tweak the state so it does not resize our children.
+  // We will do that.
+  ReflowChildFlags oldFlags = aState.LayoutFlags();
+  aState.SetLayoutFlags(ReflowChildFlags::NoSizeView);
+
+  // do a normal layout
+  nsresult rv = nsBoxFrame::DoXULLayout(aState);
+
+  // <deck> and <tabpanels> other than our browser's tab shouldn't have any
+  // <browser> or <iframe> to avoid running into troubles with Fission.
+  MOZ_ASSERT(
+      (mContent->IsXULElement(nsGkAtoms::tabpanels) &&
+       mContent->AsElement()->AttrValueIs(kNameSpaceID_None, nsGkAtoms::id,
+#ifdef MOZ_THUNDERBIRD
+                                          u"tabpanelcontainer"_ns,
+#else
+                                          u"tabbrowser-tabpanels"_ns,
+#endif
+                                          eCaseMatters)) ||
+      !HasPossiblyRemoteContents());
+
+  // run though each child. Hide all but the selected one
+  nsIFrame* box = nsIFrame::GetChildXULBox(this);
+
+  nscoord count = 0;
+  while (box) {
+    // make collapsed children not show up
+    if (count != mIndex) {
+      HideBox(box);
+    } else {
+      ShowBox(box);
+    }
+    box = GetNextXULBox(box);
+    count++;
+  }
+
+  aState.SetLayoutFlags(oldFlags);
+
+  return rv;
+}
+
+bool nsDeckFrame::HasPossiblyRemoteContents() const {
+  auto hasRemoteOrMayChangeRemoteNessAttribute =
+      [](dom::Element& aElement) -> bool {
+    return (aElement.AttrValueIs(kNameSpaceID_None, nsGkAtoms::remote,
+                                 nsGkAtoms::_true, eCaseMatters) ||
+            aElement.HasAttribute(u"maychangeremoteness"_ns));
+  };
+
+  for (nsIContent* node = mContent; node; node = node->GetNextNode(mContent)) {
+    if ((node->IsXULElement(nsGkAtoms::browser) ||
+         node->IsHTMLElement(nsGkAtoms::iframe)) &&
+        hasRemoteOrMayChangeRemoteNessAttribute(*(node->AsElement()))) {
+      return true;
+    }
+  }
+  return false;
+}

layout/xul/nsDeckFrame.h

@@ -0,0 +1,78 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+
+  Eric D Vaughan
+  A frame that can have multiple children. Only one child may be displayed at
+one time. So the can be flipped though like a deck of cards.
+
+**/
+
+#ifndef nsDeckFrame_h___
+#define nsDeckFrame_h___
+
+#include "mozilla/Attributes.h"
+#include "nsBoxFrame.h"
+
+namespace mozilla {
+class PresShell;
+}  // namespace mozilla
+
+class nsDeckFrame final : public nsBoxFrame {
+ public:
+  NS_DECL_QUERYFRAME
+  NS_DECL_FRAMEARENA_HELPERS(nsDeckFrame)
+
+  friend nsIFrame* NS_NewDeckFrame(mozilla::PresShell* aPresShell,
+                                   ComputedStyle* aStyle);
+
+  virtual nsresult AttributeChanged(int32_t aNameSpaceID, nsAtom* aAttribute,
+                                    int32_t aModType) override;
+
+  NS_IMETHOD DoXULLayout(nsBoxLayoutState& aState) override;
+
+  virtual void BuildDisplayList(nsDisplayListBuilder* aBuilder,
+                                const nsDisplayListSet& aLists) override;
+
+  virtual void RemoveFrame(ChildListID aListID, nsIFrame* aOldFrame) override;
+
+  virtual void BuildDisplayListForChildren(
+      nsDisplayListBuilder* aBuilder, const nsDisplayListSet& aLists) override;
+
+  virtual void Init(nsIContent* aContent, nsContainerFrame* aParent,
+                    nsIFrame* aPrevInFlow) override;
+
+#ifdef DEBUG_FRAME_DUMP
+  virtual nsresult GetFrameName(nsAString& aResult) const override {
+    return MakeFrameName(u"Deck"_ns, aResult);
+  }
+#endif
+
+  explicit nsDeckFrame(ComputedStyle* aStyle, nsPresContext* aPresContext);
+
+  nsIFrame* GetSelectedBox();
+
+  // Returns whether this frame has any <browser> or <iframe> elements.
+  // Note that this function traverses down all descendants so this function
+  // should be used only in debug builds.
+  bool HasPossiblyRemoteContents() const;
+
+ protected:
+  void IndexChanged();
+  int32_t GetSelectedIndex();
+  void HideBox(nsIFrame* aBox);
+  void ShowBox(nsIFrame* aBox);
+
+ private:
+  int32_t mIndex = 0;
+  nsIFrame* mSelectedBoxCache = nullptr;
+
+  void Animate(nsIFrame*, bool);
+
+};  // class nsDeckFrame
+
+#endif

layout/xul/nsDocElementBoxFrame.cpp

@@ -15,6 +15,7 @@
 #include "nsStyleConsts.h"
 #include "nsGkAtoms.h"
 #include "nsBoxFrame.h"
+#include "nsStackLayout.h"
 #include "nsIAnonymousContentCreator.h"
 #include "nsNodeInfoManager.h"
 #include "nsContentCreatorFunctions.h"

layout/xul/nsRootBoxFrame.cpp

@@ -9,6 +9,7 @@
 #include "nsGkAtoms.h"
 #include "nsBoxFrame.h"
 #include "nsDisplayList.h"
+#include "nsStackLayout.h"
 #include "nsIPopupContainer.h"
 #include "nsIContent.h"
 #include "nsFrameManager.h"

layout/xul/nsStackLayout.cpp

@@ -0,0 +1,209 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//
+// Eric Vaughan
+// Netscape Communications
+//
+// See documentation in associated header file
+//
+
+#include "nsStackLayout.h"
+#include "nsCOMPtr.h"
+#include "nsBoxLayoutState.h"
+#include "nsBoxFrame.h"
+#include "nsGkAtoms.h"
+#include "nsIContent.h"
+#include "nsNameSpaceManager.h"
+
+using namespace mozilla;
+
+nsBoxLayout* nsStackLayout::gInstance = nullptr;
+
+nsresult NS_NewStackLayout(nsCOMPtr<nsBoxLayout>& aNewLayout) {
+  if (!nsStackLayout::gInstance) {
+    nsStackLayout::gInstance = new nsStackLayout();
+    NS_IF_ADDREF(nsStackLayout::gInstance);
+  }
+  // we have not instance variables so just return our static one.
+  aNewLayout = nsStackLayout::gInstance;
+  return NS_OK;
+}
+
+/*static*/
+void nsStackLayout::Shutdown() { NS_IF_RELEASE(gInstance); }
+
+nsStackLayout::nsStackLayout() = default;
+
+/*
+ * Sizing: we are as wide as the widest child
+ * we are tall as the tallest child.
+ */
+
+nsSize nsStackLayout::GetXULPrefSize(nsIFrame* aBox, nsBoxLayoutState& aState) {
+  nsSize prefSize(0, 0);
+
+  nsIFrame* child = nsIFrame::GetChildXULBox(aBox);
+  while (child) {
+    nsSize pref = child->GetXULPrefSize(aState);
+
+    AddXULMargin(child, pref);
+
+    if (pref.width > prefSize.width) {
+      prefSize.width = pref.width;
+    }
+    if (pref.height > prefSize.height) {
+      prefSize.height = pref.height;
+    }
+
+    child = nsIFrame::GetNextXULBox(child);
+  }
+
+  AddXULBorderAndPadding(aBox, prefSize);
+
+  return prefSize;
+}
+
+nsSize nsStackLayout::GetXULMinSize(nsIFrame* aBox, nsBoxLayoutState& aState) {
+  nsSize minSize(0, 0);
+
+  nsIFrame* child = nsIFrame::GetChildXULBox(aBox);
+  while (child) {
+    nsSize min = child->GetXULMinSize(aState);
+
+    AddXULMargin(child, min);
+
+    if (min.width > minSize.width) {
+      minSize.width = min.width;
+    }
+    if (min.height > minSize.height) {
+      minSize.height = min.height;
+    }
+
+    child = nsIFrame::GetNextXULBox(child);
+  }
+
+  AddXULBorderAndPadding(aBox, minSize);
+
+  return minSize;
+}
+
+nsSize nsStackLayout::GetXULMaxSize(nsIFrame* aBox, nsBoxLayoutState& aState) {
+  nsSize maxSize(NS_UNCONSTRAINEDSIZE, NS_UNCONSTRAINEDSIZE);
+
+  nsIFrame* child = nsIFrame::GetChildXULBox(aBox);
+  while (child) {
+    nsSize min = child->GetXULMinSize(aState);
+    nsSize max = child->GetXULMaxSize(aState);
+
+    max = nsIFrame::XULBoundsCheckMinMax(min, max);
+
+    AddXULMargin(child, max);
+
+    if (max.width < maxSize.width) {
+      maxSize.width = max.width;
+    }
+    if (max.height < maxSize.height) {
+      maxSize.height = max.height;
+    }
+
+    child = nsIFrame::GetNextXULBox(child);
+  }
+
+  AddXULBorderAndPadding(aBox, maxSize);
+
+  return maxSize;
+}
+
+nscoord nsStackLayout::GetAscent(nsIFrame* aBox, nsBoxLayoutState& aState) {
+  nscoord vAscent = 0;
+
+  nsIFrame* child = nsIFrame::GetChildXULBox(aBox);
+  while (child) {
+    nscoord ascent = child->GetXULBoxAscent(aState);
+    nsMargin margin;
+    child->GetXULMargin(margin);
+    ascent += margin.top;
+    if (ascent > vAscent) vAscent = ascent;
+
+    child = nsIFrame::GetNextXULBox(child);
+  }
+
+  return vAscent;
+}
+
+NS_IMETHODIMP
+nsStackLayout::XULLayout(nsIFrame* aBox, nsBoxLayoutState& aState) {
+  nsRect clientRect;
+  aBox->GetXULClientRect(clientRect);
+
+  bool grow;
+
+  do {
+    nsIFrame* child = nsIFrame::GetChildXULBox(aBox);
+    grow = false;
+
+    while (child) {
+      nsMargin margin;
+      child->GetXULMargin(margin);
+      nsRect childRect(clientRect);
+      childRect.Deflate(margin);
+
+      if (childRect.width < 0) childRect.width = 0;
+
+      if (childRect.height < 0) childRect.height = 0;
+
+      nsRect oldRect(child->GetRect());
+      bool sizeChanged = !oldRect.IsEqualEdges(childRect);
+
+      // only lay out dirty children or children whose sizes have changed
+      if (sizeChanged || child->IsSubtreeDirty()) {
+        // add in the child's margin
+        nsMargin margin;
+        child->GetXULMargin(margin);
+
+        // Now place the child.
+        child->SetXULBounds(aState, childRect);
+
+        // Flow the child.
+        child->XULLayout(aState);
+
+        // Get the child's new rect.
+        childRect = child->GetRect();
+        childRect.Inflate(margin);
+
+        // Did the child push back on us and get bigger?
+        if (childRect.width > clientRect.width) {
+          clientRect.width = childRect.width;
+          grow = true;
+        }
+
+        if (childRect.height > clientRect.height) {
+          clientRect.height = childRect.height;
+          grow = true;
+        }
+      }
+
+      child = nsIFrame::GetNextXULBox(child);
+    }
+  } while (grow);
+
+  // if some HTML inside us got bigger we need to force ourselves to
+  // get bigger
+  nsRect bounds(aBox->GetRect());
+  nsMargin bp;
+  aBox->GetXULBorderAndPadding(bp);
+  clientRect.Inflate(bp);
+
+  if (clientRect.width > bounds.width || clientRect.height > bounds.height) {
+    if (clientRect.width > bounds.width) bounds.width = clientRect.width;
+    if (clientRect.height > bounds.height) bounds.height = clientRect.height;
+
+    aBox->SetXULBounds(aState, bounds);
+  }
+
+  return NS_OK;
+}

layout/xul/nsStackLayout.h

@@ -0,0 +1,48 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+
+  Eric D Vaughan
+  A frame that can have multiple children. Only one child may be displayed at
+one time. So the can be flipped though like a deck of cards.
+
+**/
+
+#ifndef nsStackLayout_h___
+#define nsStackLayout_h___
+
+#include "mozilla/Attributes.h"
+#include "nsBoxLayout.h"
+#include "nsCOMPtr.h"
+#include "nsCoord.h"
+
+nsresult NS_NewStackLayout(nsCOMPtr<nsBoxLayout>& aNewLayout);
+
+class nsStackLayout : public nsBoxLayout {
+ public:
+  friend nsresult NS_NewStackLayout(nsCOMPtr<nsBoxLayout>& aNewLayout);
+  static void Shutdown();
+
+  nsStackLayout();
+
+  NS_IMETHOD XULLayout(nsIFrame* aBox, nsBoxLayoutState& aState) override;
+
+  virtual nsSize GetXULPrefSize(nsIFrame* aBox,
+                                nsBoxLayoutState& aBoxLayoutState) override;
+  virtual nsSize GetXULMinSize(nsIFrame* aBox,
+                               nsBoxLayoutState& aBoxLayoutState) override;
+  virtual nsSize GetXULMaxSize(nsIFrame* aBox,
+                               nsBoxLayoutState& aBoxLayoutState) override;
+  virtual nscoord GetAscent(nsIFrame* aBox,
+                            nsBoxLayoutState& aBoxLayoutState) override;
+
+ private:
+  static nsBoxLayout* gInstance;
+
+};  // class nsStackLayout
+
+#endif

servo/components/style/properties/data.py

@@ -487,7 +487,7 @@ class Longhand(Property):
                 "LineBreak",
                 "LineClamp",
                 "MasonryAutoFlow",
-                "BoolInteger",
+                "MozForceBrokenImageIcon",
                 "text::MozControlCharacterVisibility",
                 "MathDepth",
                 "MozScriptMinSize",

servo/components/style/properties/longhands/ui.mako.rs

@@ -108,23 +108,11 @@ ${helpers.predefined_type(
     enabled_in="chrome",
 )}
 
-// Hack to allow chrome to hide stuff only visually (without hiding it from
-// a11y).
-${helpers.predefined_type(
-    "-moz-subtree-hidden-only-visually",
-    "BoolInteger",
-    "computed::BoolInteger::zero()",
-    engines="gecko",
-    animation_value_type="discrete",
-    spec="None (Nonstandard internal property)",
-    enabled_in="chrome",
-)}
-
 // TODO(emilio): Probably also should be hidden from content.
 ${helpers.predefined_type(
     "-moz-force-broken-image-icon",
-    "BoolInteger",
-    "computed::BoolInteger::zero()",
+    "MozForceBrokenImageIcon",
+    "computed::MozForceBrokenImageIcon::false_value()",
     engines="gecko",
     animation_value_type="discrete",
     spec="None (Nonstandard Firefox-only property)",

servo/components/style/values/computed/mod.rs

@@ -97,7 +97,7 @@ pub use self::transform::{Rotate, Scale, Transform, TransformOperation};
 pub use self::transform::{TransformOrigin, TransformStyle, Translate};
 #[cfg(feature = "gecko")]
 pub use self::ui::CursorImage;
-pub use self::ui::{Cursor, BoolInteger, UserSelect};
+pub use self::ui::{Cursor, MozForceBrokenImageIcon, UserSelect};
 pub use super::specified::TextTransform;
 pub use super::specified::ViewportVariant;
 pub use super::specified::{BorderStyle, TextDecorationLine};

servo/components/style/values/computed/ui.rs

@@ -10,7 +10,7 @@ use crate::values::computed::Number;
 use crate::values::generics::ui as generics;
 
 pub use crate::values::specified::ui::CursorKind;
-pub use crate::values::specified::ui::{BoolInteger, UserSelect};
+pub use crate::values::specified::ui::{MozForceBrokenImageIcon, UserSelect};
 
 /// A computed value for the `cursor` property.
 pub type Cursor = generics::GenericCursor<CursorImage>;

servo/components/style/values/specified/box.rs

@@ -101,6 +101,8 @@ pub enum DisplayInside {
     #[cfg(feature = "gecko")]
     MozBox,
     #[cfg(feature = "gecko")]
+    MozDeck,
+    #[cfg(feature = "gecko")]
     MozPopup,
 }
 
@@ -214,6 +216,8 @@ impl Display {
     #[cfg(feature = "gecko")]
     pub const MozInlineBox: Self = Self::new(DisplayOutside::Inline, DisplayInside::MozBox);
     #[cfg(feature = "gecko")]
+    pub const MozDeck: Self = Self::new(DisplayOutside::XUL, DisplayInside::MozDeck);
+    #[cfg(feature = "gecko")]
     pub const MozPopup: Self = Self::new(DisplayOutside::XUL, DisplayInside::MozPopup);
 
     /// Make a raw display value from <display-outside> and <display-inside> values.
@@ -594,6 +598,8 @@ impl Parse for Display {
             #[cfg(feature = "gecko")]
             "-moz-inline-box" if moz_display_values_enabled(context) => Display::MozInlineBox,
             #[cfg(feature = "gecko")]
+            "-moz-deck" if moz_display_values_enabled(context) => Display::MozDeck,
+            #[cfg(feature = "gecko")]
             "-moz-popup" if moz_display_values_enabled(context) => Display::MozPopup,
         })
     }

servo/components/style/values/specified/mod.rs

@@ -97,7 +97,7 @@ pub use self::transform::{Rotate, Scale, Transform};
 pub use self::transform::{TransformOrigin, TransformStyle, Translate};
 #[cfg(feature = "gecko")]
 pub use self::ui::CursorImage;
-pub use self::ui::{Cursor, BoolInteger, UserSelect};
+pub use self::ui::{Cursor, MozForceBrokenImageIcon, UserSelect};
 pub use super::generics::grid::GridTemplateComponent as GenericGridTemplateComponent;
 
 #[cfg(feature = "gecko")]

servo/components/style/values/specified/ui.rs

@@ -88,32 +88,31 @@ impl SpecifiedValueInfo for CursorImage {
     ToResolvedValue,
     ToShmem,
 )]
-#[repr(transparent)]
-pub struct BoolInteger(pub bool);
+pub struct MozForceBrokenImageIcon(pub bool);
 
-impl BoolInteger {
-    /// Returns 0
+impl MozForceBrokenImageIcon {
+    /// Return initial value of -moz-force-broken-image-icon which is false.
     #[inline]
-    pub fn zero() -> Self {
-        Self(false)
+    pub fn false_value() -> MozForceBrokenImageIcon {
+        MozForceBrokenImageIcon(false)
     }
 }
 
-impl Parse for BoolInteger {
+impl Parse for MozForceBrokenImageIcon {
     fn parse<'i, 't>(
         _context: &ParserContext,
         input: &mut Parser<'i, 't>,
-    ) -> Result<Self, ParseError<'i>> {
+    ) -> Result<MozForceBrokenImageIcon, ParseError<'i>> {
         // We intentionally don't support calc values here.
         match input.expect_integer()? {
-            0 => Ok(Self(false)),
-            1 => Ok(Self(true)),
+            0 => Ok(MozForceBrokenImageIcon(false)),
+            1 => Ok(MozForceBrokenImageIcon(true)),
             _ => Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError)),
         }
     }
 }
 
-impl ToCss for BoolInteger {
+impl ToCss for MozForceBrokenImageIcon {
     fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
     where
         W: Write,
@@ -122,6 +121,22 @@ impl ToCss for BoolInteger {
     }
 }
 
+impl From<u8> for MozForceBrokenImageIcon {
+    fn from(bits: u8) -> MozForceBrokenImageIcon {
+        MozForceBrokenImageIcon(bits == 1)
+    }
+}
+
+impl From<MozForceBrokenImageIcon> for u8 {
+    fn from(v: MozForceBrokenImageIcon) -> u8 {
+        if v.0 {
+            1
+        } else {
+            0
+        }
+    }
+}
+
 /// A specified value for `scrollbar-color` property
 pub type ScrollbarColor = generics::ScrollbarColor<Color>;
 

servo/ports/geckolib/cbindgen.toml

@@ -79,7 +79,6 @@ include = [
   "BreakBetween",
   "BreakWithin",
   "BorderStyle",
-  "BoolInteger",
   "OutlineStyle",
   "CaptionSide",
   "FontSizeAdjust",

toolkit/content/tests/chrome/test_custom_element_base.xhtml

@@ -113,7 +113,7 @@
     ok(deck instanceof MozXULElement, "instance of MozXULElement");
     ok(XULElement.isInstance(deck), "instance of XULElement");
     is(deck.id, "foo", "attribute set");
-    is(deck.selectedIndex, 0, "Custom Element is property attached");
+    is(deck.selectedIndex, "0", "Custom Element is property attached");
     deck.remove();
 
     info("Checking that whitespace text is removed but non-whitespace text isn't");

toolkit/content/tests/chrome/test_deck.xhtml

@@ -5,13 +5,14 @@
   XUL Widget Test for deck
   -->
 <window title="Deck Test"
+        onload="setTimeout(run_tests, 0);"
         xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
   <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>      
   <script src="chrome://mochikit/content/tests/SimpleTest/EventUtils.js"></script>      
 
 <deck id="deck1" style="padding-top: 5px; padding-bottom: 12px;">
   <button id="d1b1" label="Button One"/>
-  <button id="d1b2" label="Button Two is larger" style="height: 80px; margin: 1px;"/>
+  <button id="d1b2" label="Button Two is larger" height="80" style="margin: 1px;"/>
 </deck>
 <deck id="deck2" selectedIndex="1">
   <button id="d2b1" label="Button One"/>
@@ -43,15 +44,19 @@
 
   <!-- test code goes here -->
   <script type="application/javascript"><![CDATA[
-add_task(async function run_tests() {
+
+SimpleTest.waitForExplicitFinish();
+
+function run_tests() {
   test_deck();
-  await test_deck_child_removal();
-});
+  test_deck_child_removal();
+  SimpleTest.finish();
+}
 
 function test_deck()
 {
   var deck = $("deck1");
-  is(deck.selectedIndex, 0, "deck one selectedIndex");
+  ok(deck.selectedIndex === '0', "deck one selectedIndex");
   // this size is the button height, 80, plus the button padding of 1px on each side,
   // plus the deck's 5px top padding and the 12px bottom padding.
   var rect = deck.getBoundingClientRect();
@@ -61,52 +66,47 @@ function test_deck()
   // change the selected page of the deck and ensure that the mouse click goes
   // to the button on that page
   deck.selectedIndex = 1;
-  is(deck.selectedIndex, 1, "deck one selectedIndex after change");
+  ok(deck.selectedIndex === '1', "deck one selectedIndex after change");
   synthesizeMouseExpectEvent(deck, 9, 9, { }, $("d1b2"), "click", "mouse on deck one after change");
 
   deck = $("deck2");
-  is(deck.selectedIndex, 1, "deck two selectedIndex");
+  ok(deck.selectedIndex === '1', "deck two selectedIndex");
   synthesizeMouseExpectEvent(deck, 9, 9, { }, $("d2b2"), "click", "mouse on deck two");
 }
 
-async function test_deck_child_removal()
+function test_deck_child_removal()
 {
   // Start with a simple case where we have two child nodes in a deck, with
   // the second child (index 1) selected. Removing the first node should
   // automatically set the selectedIndex at 0.
   let deck = $("deck3");
   let child = $("d3b1");
-  is(deck.selectedIndex, 1, "Should have the deck element at index 1 selected");
+  is(deck.selectedIndex, "1", "Should have the deck element at index 1 selected");
 
   // Remove the child at the 0th index. The deck should automatically
   // set the selectedIndex to "0".
   child.remove();
-
-  await Promise.resolve();
-
-  is(deck.selectedIndex, 0, "Should have the deck element at index 0 selected");
+  is(deck.selectedIndex, "0", "Should have the deck element at index 0 selected");
 
   // Now scale it up by using a deck with 7 child nodes, and remove the
   // first three, making sure that the selectedIndex is decremented
   // each time.
   deck = $("deck4");
   let expectedIndex = 5;
-  is(deck.selectedIndex, expectedIndex,
+  is(deck.selectedIndex, String(expectedIndex),
      "Should have the deck element at index " + expectedIndex + " selected");
 
   for (let i = 0; i < 3; ++i) {
     deck.firstChild.remove();
     expectedIndex--;
-    await Promise.resolve();
-    is(deck.selectedIndex, expectedIndex,
+    is(deck.selectedIndex, String(expectedIndex),
        "Should have the deck element at index " + expectedIndex + " selected");
   }
 
   // Check that removing the currently selected node doesn't change
   // behaviour.
   deck.childNodes[expectedIndex].remove();
-  await Promise.resolve();
-  is(deck.selectedIndex, expectedIndex,
+  is(deck.selectedIndex, String(expectedIndex),
      "The selectedIndex should not change when removing the node " +
      "at the selected index.");
 
@@ -114,16 +114,14 @@ async function test_deck_child_removal()
   // nodes at indexes greater than the selected node.
   deck = $("deck5");
   expectedIndex = 2;
-  await Promise.resolve();
-  is(deck.selectedIndex, expectedIndex,
+  is(deck.selectedIndex, String(expectedIndex),
      "Should have the deck element at index " + expectedIndex + " selected");
 
   // And then remove all of the nodes, starting from last to first, making
   // sure that the selectedIndex does not change.
   while (deck.lastChild) {
     deck.lastChild.remove();
-    await Promise.resolve();
-    is(deck.selectedIndex, expectedIndex,
+    is(deck.selectedIndex, String(expectedIndex),
        "Should have the deck element at index " + expectedIndex + " selected");
   }
 }

toolkit/content/widgets/general.js

@@ -7,6 +7,40 @@
 // This is loaded into chrome windows with the subscript loader. Wrap in
 // a block to prevent accidentally leaking globals onto `window`.
 {
+  class MozDeck extends MozXULElement {
+    set selectedIndex(val) {
+      if (this.selectedIndex == val) {
+        return;
+      }
+      this.setAttribute("selectedIndex", val);
+      var event = document.createEvent("Events");
+      event.initEvent("select", true, true);
+      this.dispatchEvent(event);
+    }
+
+    get selectedIndex() {
+      return this.getAttribute("selectedIndex") || "0";
+    }
+
+    set selectedPanel(val) {
+      var selectedIndex = -1;
+      for (
+        var panel = val;
+        panel != null;
+        panel = panel.previousElementSibling
+      ) {
+        ++selectedIndex;
+      }
+      this.selectedIndex = selectedIndex;
+    }
+
+    get selectedPanel() {
+      return this.children[this.selectedIndex];
+    }
+  }
+
+  customElements.define("deck", MozDeck);
+
   class MozDropmarker extends MozXULElement {
     constructor() {
       super();

toolkit/content/widgets/tabbox.js

@@ -158,107 +158,14 @@
 
   customElements.define("tabbox", MozTabbox);
 
-  class MozDeck extends MozXULElement {
-    get isAsync() {
-      return this.getAttribute("async") == "true";
-    }
-
+  class MozTabpanels extends MozXULElement {
     connectedCallback() {
       if (this.delayConnectedCallback()) {
         return;
       }
-      this._selectedPanel = null;
-      this._inAsyncOperation = false;
 
-      let selectCurrentIndex = () => {
-        // Try to select the new node if any.
-        let index = this.selectedIndex;
-        let oldPanel = this._selectedPanel;
-        this._selectedPanel = this.children.item(index) || null;
-        this.updateSelectedIndex(index, oldPanel);
-      };
-
-      this._mutationObserver = new MutationObserver(records => {
-        let anyRemovals = records.some(record => !!record.removedNodes.length);
-        if (anyRemovals) {
-          // Try to keep the current selected panel in-place first.
-          let index = Array.from(this.children).indexOf(this._selectedPanel);
-          if (index != -1) {
-            // Try to keep the same node selected.
-            this.setAttribute("selectedIndex", index);
-          }
-        }
-        // Select the current index if needed in case mutations have made that
-        // available where it wasn't before.
-        if (!this._inAsyncOperation) {
-          selectCurrentIndex();
-        }
-      });
-
-      this._mutationObserver.observe(this, {
-        childList: true,
-      });
-
-      selectCurrentIndex();
-    }
-
-    disconnectedCallback() {
-      this._mutationObserver?.disconnect();
-      this._mutationObserver = null;
-    }
-
-    updateSelectedIndex(
-      val,
-      oldPanel = this.querySelector(":scope > .deck-selected")
-    ) {
-      this._inAsyncOperation = false;
-      if (oldPanel != this._selectedPanel) {
-        oldPanel?.classList.remove("deck-selected");
-        this._selectedPanel?.classList.add("deck-selected");
-      }
-      this.setAttribute("selectedIndex", val);
-    }
-
-    set selectedIndex(val) {
-      if (val < 0 || val >= this.children.length) {
-        return;
-      }
-
-      let oldPanel = this._selectedPanel;
-      this._selectedPanel = this.children[val];
-
-      this._inAsyncOperation = this.isAsync;
-      if (!this._inAsyncOperation) {
-        this.updateSelectedIndex(val, oldPanel);
-      }
-
-      if (this._selectedPanel != oldPanel) {
-        let event = document.createEvent("Events");
-        event.initEvent("select", true, true);
-        this.dispatchEvent(event);
-      }
-    }
-
-    get selectedIndex() {
-      let indexStr = this.getAttribute("selectedIndex");
-      return indexStr ? parseInt(indexStr) : 0;
-    }
-
-    set selectedPanel(val) {
-      this.selectedIndex = Array.from(this.children).indexOf(val);
-    }
-
-    get selectedPanel() {
-      return this._selectedPanel;
-    }
-  }
-
-  customElements.define("deck", MozDeck);
-
-  class MozTabpanels extends MozDeck {
-    constructor() {
-      super();
       this._tabbox = null;
+      this._selectedPanel = this.children.item(this.selectedIndex);
     }
 
     get tabbox() {
@@ -279,6 +186,46 @@
       return (this._tabbox = parent);
     }
 
+    set selectedIndex(val) {
+      if (val < 0 || val >= this.children.length) {
+        return;
+      }
+
+      let panel = this._selectedPanel;
+      this._selectedPanel = this.children[val];
+
+      if (this.getAttribute("async") != "true") {
+        this.setAttribute("selectedIndex", val);
+      }
+
+      if (this._selectedPanel != panel) {
+        let event = document.createEvent("Events");
+        event.initEvent("select", true, true);
+        this.dispatchEvent(event);
+      }
+    }
+
+    get selectedIndex() {
+      let indexStr = this.getAttribute("selectedIndex");
+      return indexStr ? parseInt(indexStr) : -1;
+    }
+
+    set selectedPanel(val) {
+      let selectedIndex = -1;
+      for (
+        let panel = val;
+        panel != null;
+        panel = panel.previousElementSibling
+      ) {
+        ++selectedIndex;
+      }
+      this.selectedIndex = selectedIndex;
+    }
+
+    get selectedPanel() {
+      return this._selectedPanel;
+    }
+
     /**
      * nsIDOMXULRelatedElement
      */
@@ -580,9 +527,7 @@
 
     set selectedIndex(val) {
       var tab = this.getItemAtIndex(val);
-      if (!tab) {
-        return;
-      }
+      if (tab) {
         for (let otherTab of this.allTabs) {
           if (otherTab != tab && otherTab.selected) {
             otherTab._selected = false;
@@ -601,6 +546,7 @@
           this.tabbox.tabpanels.selectedPanel = linkedPanel;
         }
       }
+    }
 
     get selectedIndex() {
       const tabs = this.allTabs;

toolkit/content/xul.css

@@ -448,34 +448,18 @@ treechildren::-moz-tree-cell(ltr) {
   direction: ltr !important;
 }
 
-/********** deck, tabpanels & stack *********/
+/********** deck & stack *********/
 
-tabpanels > *|*:not(:-moz-native-anonymous) {
-  /* tabpanels is special: we want to avoid displaying them, but we still want
-   * the hidden children to be accessible */
-  -moz-subtree-hidden-only-visually: 1;
+deck {
+  display: -moz-deck;
 }
 
-deck > *|*:not(:-moz-native-anonymous) {
-  visibility: hidden;
-}
-
-tabpanels > .deck-selected,
-deck > .deck-selected {
-  -moz-subtree-hidden-only-visually: 0;
-  visibility: inherit;
-}
-
-tabpanels,
-deck,
 stack {
   display: grid;
   position: relative;
 }
 
-/* We shouldn't style native anonymous children like scrollbars or what not. */
-tabpanels > *|*:not(:-moz-native-anonymous),
-deck > *|*:not(:-moz-native-anonymous),
+/* We shouldn't style native anonymous children like scrollbars or what not */
 stack > *|*:not(:-moz-native-anonymous) {
   grid-area: 1 / 1;
   z-index: 0;
@@ -505,6 +489,10 @@ tab {
   -moz-box-pack: center;
 }
 
+tabpanels {
+  display: -moz-deck;
+}
+
 /********** tooltip *********/
 
 tooltip[titletip="true"] {

toolkit/themes/osx/global/tabbox.css

@@ -26,9 +26,6 @@ tabs {
   padding: 0 10px;
   margin-bottom: -12px;
   position: relative;
-  /* Needs to sort on top of the tabbox, which is a grid container (and thus
-   * causes pseudo stacking contexts to be created) */
-  z-index: 1;
 }
 
 tab {