15 files changed, 111 insertions, 19 deletions
diff --git a/dom/html/HTMLDetailsElement.cpp b/dom/html/HTMLDetailsElement.cpp
index 9d4dd89c2a..74479b8d90 100644
--- a/dom/html/HTMLDetailsElement.cpp
+++ b/dom/html/HTMLDetailsElement.cpp
@@ -6,11 +6,39 @@
 #include "mozilla/dom/HTMLDetailsElement.h"
 
 #include "mozilla/dom/HTMLDetailsElementBinding.h"
-NS_IMPL_NS_NEW_HTML_ELEMENT(Details)
+#include "mozilla/dom/HTMLUnknownElement.h"
+#include "mozilla/Preferences.h"
+
+// Expand NS_IMPL_NS_NEW_HTML_ELEMENT(Details) to add pref check.
+nsGenericHTMLElement*
+NS_NewHTMLDetailsElement(already_AddRefed<mozilla::dom::NodeInfo>&& aNodeInfo,
+                         mozilla::dom::FromParser aFromParser)
+{
+  if (!mozilla::dom::HTMLDetailsElement::IsDetailsEnabled()) {
+    return new mozilla::dom::HTMLUnknownElement(aNodeInfo);
+  }
+
+  return new mozilla::dom::HTMLDetailsElement(aNodeInfo);
+}
 
 namespace mozilla {
 namespace dom {
 
+/* static */ bool
+HTMLDetailsElement::IsDetailsEnabled()
+{
+  static bool isDetailsEnabled = false;
+  static bool added = false;
+
+  if (!added) {
+    Preferences::AddBoolVarCache(&isDetailsEnabled,
+                                 "dom.details_element.enabled");
+    added = true;
+  }
+
+  return isDetailsEnabled;
+}
+
 HTMLDetailsElement::~HTMLDetailsElement()
 {
 }
diff --git a/dom/html/HTMLDetailsElement.h b/dom/html/HTMLDetailsElement.h
index 4575ed888d..10e70784c6 100644
--- a/dom/html/HTMLDetailsElement.h
+++ b/dom/html/HTMLDetailsElement.h
@@ -23,6 +23,8 @@ class HTMLDetailsElement final : public nsGenericHTMLElement
 public:
   using NodeInfo = mozilla::dom::NodeInfo;
 
+  static bool IsDetailsEnabled();
+
   explicit HTMLDetailsElement(already_AddRefed<NodeInfo>& aNodeInfo)
     : nsGenericHTMLElement(aNodeInfo)
   {
diff --git a/dom/html/HTMLSummaryElement.cpp b/dom/html/HTMLSummaryElement.cpp
index 42ead6b87f..ee3c07b20b 100644
--- a/dom/html/HTMLSummaryElement.cpp
+++ b/dom/html/HTMLSummaryElement.cpp
@@ -14,7 +14,17 @@
 #include "mozilla/TextEvents.h"
 #include "nsFocusManager.h"
 
-NS_IMPL_NS_NEW_HTML_ELEMENT(Summary)
+// Expand NS_IMPL_NS_NEW_HTML_ELEMENT(Summary) to add pref check.
+nsGenericHTMLElement*
+NS_NewHTMLSummaryElement(already_AddRefed<mozilla::dom::NodeInfo>&& aNodeInfo,
+                         mozilla::dom::FromParser aFromParser)
+{
+  if (!mozilla::dom::HTMLDetailsElement::IsDetailsEnabled()) {
+    return new mozilla::dom::HTMLUnknownElement(aNodeInfo);
+  }
+
+  return new mozilla::dom::HTMLSummaryElement(aNodeInfo);
+}
 
 namespace mozilla {
 namespace dom {
diff --git a/dom/webidl/EventHandler.webidl b/dom/webidl/EventHandler.webidl
index e7dc4931bd..f7acb66ef4 100644
--- a/dom/webidl/EventHandler.webidl
+++ b/dom/webidl/EventHandler.webidl
@@ -95,6 +95,7 @@ interface GlobalEventHandlers {
            [Pref="dom.select_events.enabled"]
            attribute EventHandler onselectstart;
 
+           [Pref="dom.details_element.enabled"]
            attribute EventHandler ontoggle;
 
            // Pointer events handlers
diff --git a/dom/webidl/HTMLDetailsElement.webidl b/dom/webidl/HTMLDetailsElement.webidl
index 04df82e30f..0ef20428f5 100644
--- a/dom/webidl/HTMLDetailsElement.webidl
+++ b/dom/webidl/HTMLDetailsElement.webidl
@@ -11,7 +11,7 @@
  * and create derivative works of this document.
  */
 
-[HTMLConstructor]
+[HTMLConstructor, Pref="dom.details_element.enabled"]
 interface HTMLDetailsElement : HTMLElement {
   [CEReactions, SetterThrows]
   attribute boolean open;
diff --git a/layout/base/nsCSSFrameConstructor.cpp b/layout/base/nsCSSFrameConstructor.cpp
index b40e6f8b61..9a0410d737 100644
--- a/layout/base/nsCSSFrameConstructor.cpp
+++ b/layout/base/nsCSSFrameConstructor.cpp
@@ -3580,6 +3580,10 @@ nsCSSFrameConstructor::FindHTMLData(Element* aElement,
     return nullptr;
   }
 
+  if (aTag == nsGkAtoms::details && !HTMLDetailsElement::IsDetailsEnabled()) {
+    return nullptr;
+  }
+
   static const FrameConstructionDataByTag sHTMLData[] = {
     SIMPLE_TAG_CHAIN(img, nsCSSFrameConstructor::FindImgData),
     SIMPLE_TAG_CHAIN(mozgeneratedcontentimage,
@@ -5791,7 +5795,7 @@ nsCSSFrameConstructor::AddFrameConstructionItemsInternal(nsFrameConstructorState
   // ::before and ::after); we always want to create "internal" anonymous
   // content.
   auto* details = HTMLDetailsElement::FromContentOrNull(parent);
-  if (details && !details->Open() &&
+  if (details && details->IsDetailsEnabled() && !details->Open() &&
       (!aContent->IsRootOfNativeAnonymousSubtree() ||
        aContent->IsGeneratedContentContainerForBefore() ||
        aContent->IsGeneratedContentContainerForAfter())) {
@@ -5959,7 +5963,7 @@ nsCSSFrameConstructor::AddFrameConstructionItemsInternal(nsFrameConstructorState
   }
 
   FrameConstructionItem* item = nullptr;
-  if (details && details->Open()) {
+  if (details && details->IsDetailsEnabled() && details->Open()) {
     auto* summary = HTMLSummaryElement::FromContentOrNull(aContent);
     if (summary && summary->IsMainSummary()) {
       // If details is open, the main summary needs to be rendered as if it is
diff --git a/layout/generic/crashtests/crashtests.list b/layout/generic/crashtests/crashtests.list
index d44d7614c1..c8fb84feb9 100644
--- a/layout/generic/crashtests/crashtests.list
+++ b/layout/generic/crashtests/crashtests.list
@@ -606,19 +606,19 @@ pref(layout.css.grid.enabled,true) load 1225376.html
 pref(layout.css.grid.enabled,true) load 1225592.html
 load 1229437-1.html
 load 1229437-2.html
-load details-containing-only-text.html
-load details-display-none-summary-1.html
-load details-display-none-summary-2.html
-load details-display-none-summary-3.html
-load details-open-overflow-auto.html
-load details-open-overflow-hidden.html
-load details-three-columns.html
+pref(dom.details_element.enabled,true) load details-containing-only-text.html
+pref(dom.details_element.enabled,true) load details-display-none-summary-1.html
+pref(dom.details_element.enabled,true) load details-display-none-summary-2.html
+pref(dom.details_element.enabled,true) load details-display-none-summary-3.html
+pref(dom.details_element.enabled,true) load details-open-overflow-auto.html
+pref(dom.details_element.enabled,true) load details-open-overflow-hidden.html
+pref(dom.details_element.enabled,true) load details-three-columns.html
 load first-letter-638937-1.html
 load first-letter-638937-2.html
 load flex-nested-abspos-1.html
 pref(dom.meta-viewport.enabled,true) test-pref(font.size.inflation.emPerLine,15) asserts(0-100) load font-inflation-762332.html # bug 762332
 load outline-on-frameset.xhtml
-load summary-position-out-of-flow.html
+pref(dom.details_element.enabled,true) load summary-position-out-of-flow.html
 load text-overflow-bug666751-1.html
 load text-overflow-bug666751-2.html
 load text-overflow-bug670564.xhtml
diff --git a/layout/generic/nsContainerFrame.cpp b/layout/generic/nsContainerFrame.cpp
index 835ba9b262..47afed9de1 100644
--- a/layout/generic/nsContainerFrame.cpp
+++ b/layout/generic/nsContainerFrame.cpp
@@ -1891,10 +1891,12 @@ nsContainerFrame::RenumberFrameAndDescendants(int32_t* aOrdinal,
   }
 
   // Do not renumber list for summary elements.
-  HTMLSummaryElement* summary =
-    HTMLSummaryElement::FromContent(kid->GetContent());
-  if (summary && summary->IsMainSummary()) {
-    return false;
+  if (HTMLDetailsElement::IsDetailsEnabled()) {
+    HTMLSummaryElement* summary =
+      HTMLSummaryElement::FromContent(kid->GetContent());
+    if (summary && summary->IsMainSummary()) {
+      return false;
+    }
   }
 
   bool kidRenumberedABullet = false;
diff --git a/layout/reftests/details-summary/disabled-no-summary-ref.html b/layout/reftests/details-summary/disabled-no-summary-ref.html
new file mode 100644
index 0000000000..6ecdbcdc0a
--- /dev/null
+++ b/layout/reftests/details-summary/disabled-no-summary-ref.html
@@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<!-- Any copyright is dedicated to the Public Domain.
+   - http://creativecommons.org/publicdomain/zero/1.0/ -->
+
+<html>
+  <body>
+    <div>
+      <p>This is the details.</p>
+    </div>
+  </body>
+</html>
diff --git a/layout/reftests/details-summary/disabled-single-summary-ref.html b/layout/reftests/details-summary/disabled-single-summary-ref.html
new file mode 100644
index 0000000000..f643af6dcd
--- /dev/null
+++ b/layout/reftests/details-summary/disabled-single-summary-ref.html
@@ -0,0 +1,12 @@
+<!DOCTYPE html>
+<!-- Any copyright is dedicated to the Public Domain.
+   - http://creativecommons.org/publicdomain/zero/1.0/ -->
+
+<html>
+  <body>
+    <div>
+      <div>Summary</div>
+      <p>This is the details.</p>
+    </div>
+  </body>
+</html>
diff --git a/layout/reftests/details-summary/reftest.list b/layout/reftests/details-summary/reftest.list
index a972cf4980..6b558ea137 100644
--- a/layout/reftests/details-summary/reftest.list
+++ b/layout/reftests/details-summary/reftest.list
@@ -1,3 +1,10 @@
+default-preferences pref(dom.details_element.enabled,true)
+
+# Disable <details> and <summary>
+pref(dom.details_element.enabled,false) == single-summary.html disabled-single-summary-ref.html
+pref(dom.details_element.enabled,false) == open-single-summary.html disabled-single-summary-ref.html
+pref(dom.details_element.enabled,false) == no-summary.html disabled-no-summary-ref.html
+
 # Basic <summary> handling
 == multiple-summary.html single-summary.html
 == open-multiple-summary.html open-multiple-summary-ref.html
diff --git a/layout/style/nsLayoutStylesheetCache.cpp b/layout/style/nsLayoutStylesheetCache.cpp
index bf87b006ca..1905d8c5cd 100644
--- a/layout/style/nsLayoutStylesheetCache.cpp
+++ b/layout/style/nsLayoutStylesheetCache.cpp
@@ -121,6 +121,11 @@ nsLayoutStylesheetCache::UASheet()
 StyleSheet*
 nsLayoutStylesheetCache::HTMLSheet()
 {
+  if (!mHTMLSheet) {
+    LoadSheetURL("resource://gre-resources/html.css",
+                 &mHTMLSheet, eAgentSheetFeatures, eCrash);
+  }
+
   return mHTMLSheet;
 }
 
@@ -316,8 +321,6 @@ nsLayoutStylesheetCache::nsLayoutStylesheetCache(StyleBackendType aType)
   // per-profile, since they're profile-invariant.
   LoadSheetURL("resource://gre-resources/counterstyles.css",
                &mCounterStylesSheet, eAgentSheetFeatures, eCrash);
-  LoadSheetURL("resource://gre-resources/html.css",
-               &mHTMLSheet, eAgentSheetFeatures, eCrash);
   LoadSheetURL("chrome://global/content/minimal-xul.css",
                &mMinimalXULSheet, eAgentSheetFeatures, eCrash);
   LoadSheetURL("resource://gre-resources/quirk.css",
@@ -378,6 +381,8 @@ nsLayoutStylesheetCache::For(StyleBackendType aType)
     //                               "layout.css.example-pref.enabled");
     Preferences::RegisterCallback(&DependentPrefChanged,
                                   "layout.css.grid.enabled");
+    Preferences::RegisterCallback(&DependentPrefChanged,
+                                  "dom.details_element.enabled");
   }
 
   return cache;
@@ -549,6 +554,7 @@ nsLayoutStylesheetCache::DependentPrefChanged(const char* aPref, void* aData)
                   gStyleCache_Servo ? &gStyleCache_Servo->sheet_ : nullptr);
 
   INVALIDATE(mUASheet);  // for layout.css.grid.enabled
+  INVALIDATE(mHTMLSheet); // for dom.details_element.enabled
 
 #undef INVALIDATE
 }
diff --git a/modules/libpref/init/all.js b/modules/libpref/init/all.js
index a24bec7a5a..3a16eef67f 100644
--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -5098,6 +5098,9 @@ pref("dom.audiochannel.mutedByDefault", false);
 // HTML <dialog> element
 pref("dom.dialog_element.enabled", false);
 
+// Enable <details> and <summary> tags.
+pref("dom.details_element.enabled", true);
+
 // Secure Element API
 #ifdef MOZ_SECUREELEMENT
 pref("dom.secureelement.enabled", false);
diff --git a/testing/web-platform/meta/html/semantics/interactive-elements/the-details-element/details.html.ini b/testing/web-platform/meta/html/semantics/interactive-elements/the-details-element/details.html.ini
new file mode 100644
index 0000000000..6ffca742cc
--- /dev/null
+++ b/testing/web-platform/meta/html/semantics/interactive-elements/the-details-element/details.html.ini
@@ -0,0 +1,3 @@
+[details.html]
+  type: testharness
+  prefs: [dom.details_element.enabled:true]
diff --git a/testing/web-platform/meta/html/semantics/interactive-elements/the-details-element/toggleEvent.html.ini b/testing/web-platform/meta/html/semantics/interactive-elements/the-details-element/toggleEvent.html.ini
new file mode 100644
index 0000000000..335ffd5b3a
--- /dev/null
+++ b/testing/web-platform/meta/html/semantics/interactive-elements/the-details-element/toggleEvent.html.ini
@@ -0,0 +1,3 @@
+[toggleEvent.html]
+  type: testharness
+  prefs: [dom.details_element.enabled:true]