From 7e46a922c154d4c1a927fa00780987ab6b693aa8 Mon Sep 17 00:00:00 2001
From: Boris Zbarsky <bzbarsky@mit.edu>
Date: Mon, 24 Dec 2012 19:35:34 -0800
Subject: [PATCH] Bug 818400.  Add a preference to control :scope and pref it
 off in release builds for now.  r=dbaron

---
 content/base/test/file_bug416317.xhtml |  34 ++++--
 layout/inspector/src/inDOMUtils.cpp    |   4 +-
 layout/style/nsCSSPseudoClassList.h    | 161 +++++++++++++------------
 layout/style/nsCSSPseudoClasses.cpp    |  25 +++-
 layout/style/nsCSSPseudoClasses.h      |   2 +-
 layout/style/nsCSSRuleProcessor.cpp    |   8 +-
 modules/libpref/src/init/all.js        |   7 ++
 7 files changed, 139 insertions(+), 102 deletions(-)

diff --git a/content/base/test/file_bug416317.xhtml b/content/base/test/file_bug416317.xhtml
index 8bbfadad3f5..564ba6925f8 100644
--- a/content/base/test/file_bug416317.xhtml
+++ b/content/base/test/file_bug416317.xhtml
@@ -100,8 +100,8 @@
     /* :root tests */
     :root { background-color: green; }
 
-    /* :-moz-scope tests */
-    :-moz-scope { background-color: green; }
+    /* :scope tests */
+    :scope { background-color: green; }
 
     /* :nth-child(n) tests */
     .nthchild1 > :nth-last-child(odd) { background-color: lime; }
@@ -226,7 +226,17 @@
     .bar. { background: red; color: yellow; }
   </span>
   <script><![CDATA[
-  window.onload = function(){
+  window.onload = function() {
+    if (window.parent && window.parent.SpecialPowers) {
+      window.parent.SpecialPowers.pushPrefEnv(
+        { 'set': [[ "layout.css.scope-pseudo.enabled", true]] },
+        doTest);
+    } else {
+      doTest();
+    }
+  }
+
+  function doTest(){
     if ( window.location.hash.indexOf("target") == -1 )
       window.location.hash = "#target";
 
@@ -544,7 +554,7 @@
         var namespaced = /\|[^=]/.test( q );
         var prepend = namespaced ? "xHTML|*#root3 " : "#root3 ";
         q = (restrict === false || restrict === ":root" ||
-             restrict === ":-moz-scope" ? "" : prepend) +
+             restrict === ":scope" ? "" : prepend) +
             q.replace(/,/g, ", " + prepend);
         var nq = q.replace(/>/g, "&gt;").replace(/</g, "&lt;");
 
@@ -576,9 +586,9 @@
             (pass ? "" : " Expected: " + extra(ids) + " Received: " + extra(results)) );
 
           // For now, don't use checkMatchesSelector when
-          // restrict === ":-moz-scope" because we have no way to hand the
+          // restrict === ":scope" because we have no way to hand the
           // right scope to it yet.
-          if (results && restrict !== ":-moz-scope")
+          if (results && restrict !== ":scope")
             checkMatchesSelector( results, q );
         }
 
@@ -641,15 +651,15 @@
 
       if ( root == document ) {
         t( ":root Selector", ":root", ["html"], false );
-        t( ":-moz-scope Selector", ":-moz-scope", ["html"], ":-moz-scope" );
+        t( ":scope Selector", ":scope", ["html"], ":scope" );
       } else {
         t( ":root Selector", ":root", [], ":root" );
         if (root.localName != "nosuchtag") {
-          t( ":-moz-scope Selector", ":-moz-scope > nosuchtag",
-             [ "outerbogustag" ], ":-moz-scope");
+          t( ":scope Selector", ":scope > nosuchtag",
+             [ "outerbogustag" ], ":scope");
         }
-        t( ":-moz-scope Selector", ":-moz-scope nosuchtag nosuchtag",
-           [ "innerbogustag" ], ":-moz-scope");
+        t( ":scope Selector", ":scope nosuchtag nosuchtag",
+           [ "innerbogustag" ], ":scope");
 
         if ( !root.parentNode ) {
           t( ":root All Selector", ":root *", [], ":root" );
@@ -659,7 +669,7 @@
       if ( root.parentNode || root == document ) {
         assert( query(":root *").length == query("*").length - (root == document ? 1 : 0), type + ": :root All Selector" );
       }
-      assert( query(":-moz-scope *").length == query("*").length - (root == document ? 1 : 0), type + ": :-moz-scope All Selector" );
+      assert( query(":scope *").length == query("*").length - (root == document ? 1 : 0), type + ": :scope All Selector" );
 
       t( "Element Selector", "p", ["firstp","ap","sndp","en","sap","first"] );
       t( "Element Selector", "body", ["body"], false );
diff --git a/layout/inspector/src/inDOMUtils.cpp b/layout/inspector/src/inDOMUtils.cpp
index 3e295776cbc..8c220ca1746 100644
--- a/layout/inspector/src/inDOMUtils.cpp
+++ b/layout/inspector/src/inDOMUtils.cpp
@@ -326,9 +326,9 @@ GetStatesForPseudoClass(const nsAString& aStatePseudo)
   // An array of the states that are relevant for various pseudoclasses.
   // XXXbz this duplicates code in nsCSSRuleProcessor
   static const nsEventStates sPseudoClassStates[] = {
-#define CSS_PSEUDO_CLASS(_name, _value) \
+#define CSS_PSEUDO_CLASS(_name, _value, _pref)	\
     nsEventStates(),
-#define CSS_STATE_PSEUDO_CLASS(_name, _value, _states) \
+#define CSS_STATE_PSEUDO_CLASS(_name, _value, _pref, _states)	\
     _states,
 #include "nsCSSPseudoClassList.h"
 #undef CSS_STATE_PSEUDO_CLASS
diff --git a/layout/style/nsCSSPseudoClassList.h b/layout/style/nsCSSPseudoClassList.h
index 807a0e3bbe9..5a8335c51d2 100644
--- a/layout/style/nsCSSPseudoClassList.h
+++ b/layout/style/nsCSSPseudoClassList.h
@@ -14,7 +14,10 @@
  * will have cruel and unusual things done to them.  The entries should
  * be kept in some sort of logical order.  The first argument to
  * CSS_PSEUDO_CLASS is the C++ identifier of the atom.  The second
- * argument is the string value of the atom.
+ * argument is the string value of the atom.  The third argument is the
+ * name of the preference controlling whether the pseudo-class is
+ * recognized by the parser, or the empty string if it's unconditional.
+ *
  * CSS_STATE_DEPENDENT_PSEUDO_CLASS and CSS_STATE_PSEUDO_CLASS also take
  * the name of the state bits that the class corresponds to.  Only one
  * of the bits needs to match for a CSS_STATE_PSEUDO_CLASS to match;
@@ -36,8 +39,8 @@
 #endif
 
 #ifndef CSS_STATE_DEPENDENT_PSEUDO_CLASS
-#define CSS_STATE_DEPENDENT_PSEUDO_CLASS(_name, _value, _bit) \
-  CSS_PSEUDO_CLASS(_name, _value)
+#define CSS_STATE_DEPENDENT_PSEUDO_CLASS(_name, _value, _pref, _bit)  \
+  CSS_PSEUDO_CLASS(_name, _value, _pref)
 #define DEFINED_CSS_STATE_DEPENDENT_PSEUDO_CLASS
 #endif
 
@@ -46,8 +49,8 @@
 #endif
 
 #ifndef CSS_STATE_PSEUDO_CLASS
-#define CSS_STATE_PSEUDO_CLASS(_name, _value, _bit) \
-  CSS_STATE_DEPENDENT_PSEUDO_CLASS(_name, _value, _bit)
+#define CSS_STATE_PSEUDO_CLASS(_name, _value, _pref, _bit)      \
+  CSS_STATE_DEPENDENT_PSEUDO_CLASS(_name, _value, _pref, _bit)
 #define DEFINED_CSS_STATE_PSEUDO_CLASS
 #endif
 
@@ -56,148 +59,148 @@
 // must be the same as the order of cases in SelectorMatches.  :not
 // must be the last CSS_PSEUDO_CLASS.
 
-CSS_PSEUDO_CLASS(empty, ":empty")
-CSS_PSEUDO_CLASS(mozOnlyWhitespace, ":-moz-only-whitespace")
-CSS_PSEUDO_CLASS(mozEmptyExceptChildrenWithLocalname, ":-moz-empty-except-children-with-localname")
-CSS_PSEUDO_CLASS(lang, ":lang")
-CSS_PSEUDO_CLASS(mozBoundElement, ":-moz-bound-element")
-CSS_PSEUDO_CLASS(root, ":root")
-CSS_PSEUDO_CLASS(any, ":-moz-any")
+CSS_PSEUDO_CLASS(empty, ":empty", "")
+CSS_PSEUDO_CLASS(mozOnlyWhitespace, ":-moz-only-whitespace", "")
+CSS_PSEUDO_CLASS(mozEmptyExceptChildrenWithLocalname, ":-moz-empty-except-children-with-localname", "")
+CSS_PSEUDO_CLASS(lang, ":lang", "")
+CSS_PSEUDO_CLASS(mozBoundElement, ":-moz-bound-element", "")
+CSS_PSEUDO_CLASS(root, ":root", "")
+CSS_PSEUDO_CLASS(any, ":-moz-any", "")
 
-CSS_PSEUDO_CLASS(firstChild, ":first-child")
-CSS_PSEUDO_CLASS(firstNode, ":-moz-first-node")
-CSS_PSEUDO_CLASS(lastChild, ":last-child")
-CSS_PSEUDO_CLASS(lastNode, ":-moz-last-node")
-CSS_PSEUDO_CLASS(onlyChild, ":only-child")
-CSS_PSEUDO_CLASS(firstOfType, ":first-of-type")
-CSS_PSEUDO_CLASS(lastOfType, ":last-of-type")
-CSS_PSEUDO_CLASS(onlyOfType, ":only-of-type")
-CSS_PSEUDO_CLASS(nthChild, ":nth-child")
-CSS_PSEUDO_CLASS(nthLastChild, ":nth-last-child")
-CSS_PSEUDO_CLASS(nthOfType, ":nth-of-type")
-CSS_PSEUDO_CLASS(nthLastOfType, ":nth-last-of-type")
+CSS_PSEUDO_CLASS(firstChild, ":first-child", "")
+CSS_PSEUDO_CLASS(firstNode, ":-moz-first-node", "")
+CSS_PSEUDO_CLASS(lastChild, ":last-child", "")
+CSS_PSEUDO_CLASS(lastNode, ":-moz-last-node", "")
+CSS_PSEUDO_CLASS(onlyChild, ":only-child", "")
+CSS_PSEUDO_CLASS(firstOfType, ":first-of-type", "")
+CSS_PSEUDO_CLASS(lastOfType, ":last-of-type", "")
+CSS_PSEUDO_CLASS(onlyOfType, ":only-of-type", "")
+CSS_PSEUDO_CLASS(nthChild, ":nth-child", "")
+CSS_PSEUDO_CLASS(nthLastChild, ":nth-last-child", "")
+CSS_PSEUDO_CLASS(nthOfType, ":nth-of-type", "")
+CSS_PSEUDO_CLASS(nthLastOfType, ":nth-last-of-type", "")
 
 // Match nodes that are HTML but not XHTML
-CSS_PSEUDO_CLASS(mozIsHTML, ":-moz-is-html")
+CSS_PSEUDO_CLASS(mozIsHTML, ":-moz-is-html", "")
 
 // Matches anything when the specified look-and-feel metric is set
-CSS_PSEUDO_CLASS(mozSystemMetric, ":-moz-system-metric")
+CSS_PSEUDO_CLASS(mozSystemMetric, ":-moz-system-metric", "")
 
 // -moz-locale-dir(ltr) and -moz-locale-dir(rtl) may be used
 // to match based on the locale's chrome direction
-CSS_PSEUDO_CLASS(mozLocaleDir, ":-moz-locale-dir")
+CSS_PSEUDO_CLASS(mozLocaleDir, ":-moz-locale-dir", "")
 
 // -moz-lwtheme may be used to match a document that has a lightweight theme
-CSS_PSEUDO_CLASS(mozLWTheme, ":-moz-lwtheme")
+CSS_PSEUDO_CLASS(mozLWTheme, ":-moz-lwtheme", "")
 
 // -moz-lwtheme-brighttext matches a document that has a dark lightweight theme
-CSS_PSEUDO_CLASS(mozLWThemeBrightText, ":-moz-lwtheme-brighttext")
+CSS_PSEUDO_CLASS(mozLWThemeBrightText, ":-moz-lwtheme-brighttext", "")
 
 // -moz-lwtheme-darktext matches a document that has a bright lightweight theme
-CSS_PSEUDO_CLASS(mozLWThemeDarkText, ":-moz-lwtheme-darktext")
+CSS_PSEUDO_CLASS(mozLWThemeDarkText, ":-moz-lwtheme-darktext", "")
 
 // Matches anything when the containing window is inactive
-CSS_PSEUDO_CLASS(mozWindowInactive, ":-moz-window-inactive")
+CSS_PSEUDO_CLASS(mozWindowInactive, ":-moz-window-inactive", "")
 
 // Matches any table elements that have a nonzero border attribute,
 // according to HTML integer attribute parsing rules.
-CSS_PSEUDO_CLASS(mozTableBorderNonzero, ":-moz-table-border-nonzero")
+CSS_PSEUDO_CLASS(mozTableBorderNonzero, ":-moz-table-border-nonzero", "")
 
 // Matches whatever the contextual reference elements are for the
 // matching operation.
-CSS_PSEUDO_CLASS(scope, ":-moz-scope")
+CSS_PSEUDO_CLASS(scope, ":scope", "layout.css.scope-pseudo.enabled")
 
 // :not needs to come at the end of the non-bit pseudo-class list, since
 // it doesn't actually get directly matched on in SelectorMatches.
-CSS_PSEUDO_CLASS(notPseudo, ":not")
+CSS_PSEUDO_CLASS(notPseudo, ":not", "")
 
 // :-moz-dir(ltr) and :-moz-dir(rtl) match elements whose resolved
 // directionality in the markup language is ltr or rtl respectively
-CSS_STATE_DEPENDENT_PSEUDO_CLASS(dir, ":-moz-dir",
+CSS_STATE_DEPENDENT_PSEUDO_CLASS(dir, ":-moz-dir", "",
                                  NS_EVENT_STATE_LTR | NS_EVENT_STATE_RTL)
 
-CSS_STATE_PSEUDO_CLASS(link, ":link", NS_EVENT_STATE_UNVISITED)
+CSS_STATE_PSEUDO_CLASS(link, ":link", "", NS_EVENT_STATE_UNVISITED)
 // what matches :link or :visited
-CSS_STATE_PSEUDO_CLASS(mozAnyLink, ":-moz-any-link",
+CSS_STATE_PSEUDO_CLASS(mozAnyLink, ":-moz-any-link", "",
                        NS_EVENT_STATE_VISITED | NS_EVENT_STATE_UNVISITED)
-CSS_STATE_PSEUDO_CLASS(visited, ":visited", NS_EVENT_STATE_VISITED)
+CSS_STATE_PSEUDO_CLASS(visited, ":visited", "", NS_EVENT_STATE_VISITED)
 
-CSS_STATE_PSEUDO_CLASS(active, ":active", NS_EVENT_STATE_ACTIVE)
-CSS_STATE_PSEUDO_CLASS(checked, ":checked", NS_EVENT_STATE_CHECKED)
-CSS_STATE_PSEUDO_CLASS(disabled, ":disabled", NS_EVENT_STATE_DISABLED)
-CSS_STATE_PSEUDO_CLASS(enabled, ":enabled", NS_EVENT_STATE_ENABLED)
-CSS_STATE_PSEUDO_CLASS(focus, ":focus", NS_EVENT_STATE_FOCUS)
-CSS_STATE_PSEUDO_CLASS(hover, ":hover", NS_EVENT_STATE_HOVER)
-CSS_STATE_PSEUDO_CLASS(mozDragOver, ":-moz-drag-over", NS_EVENT_STATE_DRAGOVER)
-CSS_STATE_PSEUDO_CLASS(target, ":target", NS_EVENT_STATE_URLTARGET)
-CSS_STATE_PSEUDO_CLASS(indeterminate, ":indeterminate",
+CSS_STATE_PSEUDO_CLASS(active, ":active", "", NS_EVENT_STATE_ACTIVE)
+CSS_STATE_PSEUDO_CLASS(checked, ":checked", "", NS_EVENT_STATE_CHECKED)
+CSS_STATE_PSEUDO_CLASS(disabled, ":disabled", "", NS_EVENT_STATE_DISABLED)
+CSS_STATE_PSEUDO_CLASS(enabled, ":enabled", "", NS_EVENT_STATE_ENABLED)
+CSS_STATE_PSEUDO_CLASS(focus, ":focus", "", NS_EVENT_STATE_FOCUS)
+CSS_STATE_PSEUDO_CLASS(hover, ":hover", "", NS_EVENT_STATE_HOVER)
+CSS_STATE_PSEUDO_CLASS(mozDragOver, ":-moz-drag-over", "", NS_EVENT_STATE_DRAGOVER)
+CSS_STATE_PSEUDO_CLASS(target, ":target", "", NS_EVENT_STATE_URLTARGET)
+CSS_STATE_PSEUDO_CLASS(indeterminate, ":indeterminate", "",
                        NS_EVENT_STATE_INDETERMINATE)
 
 // Matches the element which is being displayed full-screen, and
 // any containing frames.
-CSS_STATE_PSEUDO_CLASS(mozFullScreen, ":-moz-full-screen", NS_EVENT_STATE_FULL_SCREEN)
+CSS_STATE_PSEUDO_CLASS(mozFullScreen, ":-moz-full-screen", "", NS_EVENT_STATE_FULL_SCREEN)
 
 // Matches any element which is an ancestor of the DOM full-screen element,
 // or an ancestor of a containing frame of the full-screen element.
-CSS_STATE_PSEUDO_CLASS(mozFullScreenAncestor, ":-moz-full-screen-ancestor", NS_EVENT_STATE_FULL_SCREEN_ANCESTOR)
+CSS_STATE_PSEUDO_CLASS(mozFullScreenAncestor, ":-moz-full-screen-ancestor", "", NS_EVENT_STATE_FULL_SCREEN_ANCESTOR)
 
 // Matches if the element is focused and should show a focus ring
-CSS_STATE_PSEUDO_CLASS(mozFocusRing, ":-moz-focusring", NS_EVENT_STATE_FOCUSRING)
+CSS_STATE_PSEUDO_CLASS(mozFocusRing, ":-moz-focusring", "", NS_EVENT_STATE_FOCUSRING)
 
 // Image, object, etc state pseudo-classes
-CSS_STATE_PSEUDO_CLASS(mozBroken, ":-moz-broken", NS_EVENT_STATE_BROKEN)
-CSS_STATE_PSEUDO_CLASS(mozUserDisabled, ":-moz-user-disabled",
+CSS_STATE_PSEUDO_CLASS(mozBroken, ":-moz-broken", "", NS_EVENT_STATE_BROKEN)
+CSS_STATE_PSEUDO_CLASS(mozUserDisabled, ":-moz-user-disabled", "",
                        NS_EVENT_STATE_USERDISABLED)
-CSS_STATE_PSEUDO_CLASS(mozSuppressed, ":-moz-suppressed",
+CSS_STATE_PSEUDO_CLASS(mozSuppressed, ":-moz-suppressed", "",
                        NS_EVENT_STATE_SUPPRESSED)
-CSS_STATE_PSEUDO_CLASS(mozLoading, ":-moz-loading", NS_EVENT_STATE_LOADING)
-CSS_STATE_PSEUDO_CLASS(mozTypeUnsupported, ":-moz-type-unsupported",
+CSS_STATE_PSEUDO_CLASS(mozLoading, ":-moz-loading", "", NS_EVENT_STATE_LOADING)
+CSS_STATE_PSEUDO_CLASS(mozTypeUnsupported, ":-moz-type-unsupported", "",
                        NS_EVENT_STATE_TYPE_UNSUPPORTED)
-CSS_STATE_PSEUDO_CLASS(mozTypeUnsupportedPlatform, ":-moz-type-unsupported-platform",
+CSS_STATE_PSEUDO_CLASS(mozTypeUnsupportedPlatform, ":-moz-type-unsupported-platform", "",
                        NS_EVENT_STATE_TYPE_UNSUPPORTED_PLATFORM)
-CSS_STATE_PSEUDO_CLASS(mozHandlerClickToPlay, ":-moz-handler-clicktoplay",
+CSS_STATE_PSEUDO_CLASS(mozHandlerClickToPlay, ":-moz-handler-clicktoplay", "",
                        NS_EVENT_STATE_TYPE_CLICK_TO_PLAY)
-CSS_STATE_PSEUDO_CLASS(mozHandlerPlayPreview, ":-moz-handler-playpreview",
+CSS_STATE_PSEUDO_CLASS(mozHandlerPlayPreview, ":-moz-handler-playpreview", "",
                        NS_EVENT_STATE_TYPE_PLAY_PREVIEW)
-CSS_STATE_PSEUDO_CLASS(mozHandlerVulnerableUpdatable, ":-moz-handler-vulnerable-updatable",
+CSS_STATE_PSEUDO_CLASS(mozHandlerVulnerableUpdatable, ":-moz-handler-vulnerable-updatable", "",
                        NS_EVENT_STATE_VULNERABLE_UPDATABLE)
-CSS_STATE_PSEUDO_CLASS(mozHandlerVulnerableNoUpdate, ":-moz-handler-vulnerable-no-update",
+CSS_STATE_PSEUDO_CLASS(mozHandlerVulnerableNoUpdate, ":-moz-handler-vulnerable-no-update", "",
                        NS_EVENT_STATE_VULNERABLE_NO_UPDATE)
-CSS_STATE_PSEUDO_CLASS(mozHandlerDisabled, ":-moz-handler-disabled",
+CSS_STATE_PSEUDO_CLASS(mozHandlerDisabled, ":-moz-handler-disabled", "",
                        NS_EVENT_STATE_HANDLER_DISABLED)
-CSS_STATE_PSEUDO_CLASS(mozHandlerBlocked, ":-moz-handler-blocked",
+CSS_STATE_PSEUDO_CLASS(mozHandlerBlocked, ":-moz-handler-blocked", "",
                        NS_EVENT_STATE_HANDLER_BLOCKED)
-CSS_STATE_PSEUDO_CLASS(mozHandlerCrashed, ":-moz-handler-crashed",
+CSS_STATE_PSEUDO_CLASS(mozHandlerCrashed, ":-moz-handler-crashed", "",
                        NS_EVENT_STATE_HANDLER_CRASHED)
 
 CSS_STATE_PSEUDO_CLASS(mozMathIncrementScriptLevel,
-                       ":-moz-math-increment-script-level",
+                       ":-moz-math-increment-script-level", "",
                        NS_EVENT_STATE_INCREMENT_SCRIPT_LEVEL)
 
 // CSS 3 UI
 // http://www.w3.org/TR/2004/CR-css3-ui-20040511/#pseudo-classes
-CSS_STATE_PSEUDO_CLASS(required, ":required", NS_EVENT_STATE_REQUIRED)
-CSS_STATE_PSEUDO_CLASS(optional, ":optional", NS_EVENT_STATE_OPTIONAL)
-CSS_STATE_PSEUDO_CLASS(valid, ":valid", NS_EVENT_STATE_VALID)
-CSS_STATE_PSEUDO_CLASS(invalid, ":invalid", NS_EVENT_STATE_INVALID)
-CSS_STATE_PSEUDO_CLASS(inRange, ":in-range", NS_EVENT_STATE_INRANGE)
-CSS_STATE_PSEUDO_CLASS(outOfRange, ":out-of-range", NS_EVENT_STATE_OUTOFRANGE)
-CSS_STATE_PSEUDO_CLASS(defaultPseudo, ":default", NS_EVENT_STATE_DEFAULT)
-CSS_STATE_PSEUDO_CLASS(mozReadOnly, ":-moz-read-only",
+CSS_STATE_PSEUDO_CLASS(required, ":required", "", NS_EVENT_STATE_REQUIRED)
+CSS_STATE_PSEUDO_CLASS(optional, ":optional", "", NS_EVENT_STATE_OPTIONAL)
+CSS_STATE_PSEUDO_CLASS(valid, ":valid", "", NS_EVENT_STATE_VALID)
+CSS_STATE_PSEUDO_CLASS(invalid, ":invalid", "", NS_EVENT_STATE_INVALID)
+CSS_STATE_PSEUDO_CLASS(inRange, ":in-range", "", NS_EVENT_STATE_INRANGE)
+CSS_STATE_PSEUDO_CLASS(outOfRange, ":out-of-range", "", NS_EVENT_STATE_OUTOFRANGE)
+CSS_STATE_PSEUDO_CLASS(defaultPseudo, ":default", "", NS_EVENT_STATE_DEFAULT)
+CSS_STATE_PSEUDO_CLASS(mozReadOnly, ":-moz-read-only", "",
                        NS_EVENT_STATE_MOZ_READONLY)
-CSS_STATE_PSEUDO_CLASS(mozReadWrite, ":-moz-read-write",
+CSS_STATE_PSEUDO_CLASS(mozReadWrite, ":-moz-read-write", "",
                        NS_EVENT_STATE_MOZ_READWRITE)
-CSS_STATE_PSEUDO_CLASS(mozSubmitInvalid, ":-moz-submit-invalid",
+CSS_STATE_PSEUDO_CLASS(mozSubmitInvalid, ":-moz-submit-invalid", "",
                        NS_EVENT_STATE_MOZ_SUBMITINVALID)
-CSS_STATE_PSEUDO_CLASS(mozUIInvalid, ":-moz-ui-invalid",
+CSS_STATE_PSEUDO_CLASS(mozUIInvalid, ":-moz-ui-invalid", "",
                        NS_EVENT_STATE_MOZ_UI_INVALID)
-CSS_STATE_PSEUDO_CLASS(mozUIValid, ":-moz-ui-valid",
+CSS_STATE_PSEUDO_CLASS(mozUIValid, ":-moz-ui-valid", "",
                        NS_EVENT_STATE_MOZ_UI_VALID)
-CSS_STATE_PSEUDO_CLASS(mozMeterOptimum, ":-moz-meter-optimum",
+CSS_STATE_PSEUDO_CLASS(mozMeterOptimum, ":-moz-meter-optimum", "",
                        NS_EVENT_STATE_OPTIMUM)
-CSS_STATE_PSEUDO_CLASS(mozMeterSubOptimum, ":-moz-meter-sub-optimum",
+CSS_STATE_PSEUDO_CLASS(mozMeterSubOptimum, ":-moz-meter-sub-optimum", "",
                        NS_EVENT_STATE_SUB_OPTIMUM)
-CSS_STATE_PSEUDO_CLASS(mozMeterSubSubOptimum, ":-moz-meter-sub-sub-optimum",
+CSS_STATE_PSEUDO_CLASS(mozMeterSubSubOptimum, ":-moz-meter-sub-sub-optimum", "",
                        NS_EVENT_STATE_SUB_SUB_OPTIMUM)
 
 #ifdef DEFINED_CSS_STATE_PSEUDO_CLASS
diff --git a/layout/style/nsCSSPseudoClasses.cpp b/layout/style/nsCSSPseudoClasses.cpp
index f04c6f5bd5e..2a601588d8f 100644
--- a/layout/style/nsCSSPseudoClasses.cpp
+++ b/layout/style/nsCSSPseudoClasses.cpp
@@ -11,29 +11,46 @@
 #include "nsAtomListUtils.h"
 #include "nsStaticAtom.h"
 #include "nsMemory.h"
+#include "mozilla/Preferences.h"
 
 using namespace mozilla;
 
 // define storage for all atoms
-#define CSS_PSEUDO_CLASS(_name, _value) static nsIAtom* sPseudoClass_##_name;
+#define CSS_PSEUDO_CLASS(_name, _value, _pref) \
+  static nsIAtom* sPseudoClass_##_name;
 #include "nsCSSPseudoClassList.h"
 #undef CSS_PSEUDO_CLASS
 
-#define CSS_PSEUDO_CLASS(name_, value_) \
+#define CSS_PSEUDO_CLASS(name_, value_, pref_)  \
   NS_STATIC_ATOM_BUFFER(name_##_buffer, value_)
 #include "nsCSSPseudoClassList.h"
 #undef CSS_PSEUDO_CLASS
 
 static const nsStaticAtom CSSPseudoClasses_info[] = {
-#define CSS_PSEUDO_CLASS(name_, value_) \
+#define CSS_PSEUDO_CLASS(name_, value_, pref_)            \
   NS_STATIC_ATOM(name_##_buffer, &sPseudoClass_##name_),
 #include "nsCSSPseudoClassList.h"
 #undef CSS_PSEUDO_CLASS
 };
 
+static bool sPseudoClassEnabled[] = {
+#define CSS_PSEUDO_CLASS(name_, value_, pref_)            \
+  true,
+#include "nsCSSPseudoClassList.h"
+#undef CSS_PSEUDO_CLASS
+};  
+
 void nsCSSPseudoClasses::AddRefAtoms()
 {
   NS_RegisterStaticAtoms(CSSPseudoClasses_info);
+  
+#define CSS_PSEUDO_CLASS(name_, value_, pref_)                               \
+  if (pref_[0]) {                                                            \
+    Preferences::AddBoolVarCache(&sPseudoClassEnabled[ePseudoClass_##name_], \
+                                 pref_);                                     \
+  }
+#include "nsCSSPseudoClassList.h"
+#undef CSS_PSEUDO_CLASS
 }
 
 bool
@@ -68,7 +85,7 @@ nsCSSPseudoClasses::GetPseudoType(nsIAtom* aAtom)
 {
   for (uint32_t i = 0; i < ArrayLength(CSSPseudoClasses_info); ++i) {
     if (*CSSPseudoClasses_info[i].mAtom == aAtom) {
-      return Type(i);
+      return sPseudoClassEnabled[i] ? Type(i) : ePseudoClass_NotPseudoClass;
     }
   }
 
diff --git a/layout/style/nsCSSPseudoClasses.h b/layout/style/nsCSSPseudoClasses.h
index bc82b90a030..4053203bfe6 100644
--- a/layout/style/nsCSSPseudoClasses.h
+++ b/layout/style/nsCSSPseudoClasses.h
@@ -16,7 +16,7 @@ public:
   static void AddRefAtoms();
 
   enum Type {
-#define CSS_PSEUDO_CLASS(_name, _value) \
+#define CSS_PSEUDO_CLASS(_name, _value, _pref)        \
     ePseudoClass_##_name,
 #include "nsCSSPseudoClassList.h"
 #undef CSS_PSEUDO_CLASS
diff --git a/layout/style/nsCSSRuleProcessor.cpp b/layout/style/nsCSSRuleProcessor.cpp
index 8156b4da72a..cc5869f86f7 100644
--- a/layout/style/nsCSSRuleProcessor.cpp
+++ b/layout/style/nsCSSRuleProcessor.cpp
@@ -1538,9 +1538,9 @@ checkGenericEmptyMatches(Element* aElement,
 
 // Arrays of the states that are relevant for various pseudoclasses.
 static const nsEventStates sPseudoClassStateDependences[] = {
-#define CSS_PSEUDO_CLASS(_name, _value) \
+#define CSS_PSEUDO_CLASS(_name, _value, _pref)  \
   nsEventStates(),
-#define CSS_STATE_DEPENDENT_PSEUDO_CLASS(_name, _value, _states)  \
+#define CSS_STATE_DEPENDENT_PSEUDO_CLASS(_name, _value, _pref, _states)  \
   _states,
 #include "nsCSSPseudoClassList.h"
 #undef CSS_STATE_DEPENDENT_PSEUDO_CLASS
@@ -1552,9 +1552,9 @@ static const nsEventStates sPseudoClassStateDependences[] = {
 };
 
 static const nsEventStates sPseudoClassStates[] = {
-#define CSS_PSEUDO_CLASS(_name, _value)         \
+#define CSS_PSEUDO_CLASS(_name, _value, _pref)  \
   nsEventStates(),
-#define CSS_STATE_PSEUDO_CLASS(_name, _value, _states) \
+#define CSS_STATE_PSEUDO_CLASS(_name, _value, _pref, _states) \
   _states,
 #include "nsCSSPseudoClassList.h"
 #undef CSS_STATE_PSEUDO_CLASS
diff --git a/modules/libpref/src/init/all.js b/modules/libpref/src/init/all.js
index cd6f4a10a1f..1b292562034 100644
--- a/modules/libpref/src/init/all.js
+++ b/modules/libpref/src/init/all.js
@@ -1661,6 +1661,13 @@ pref("layout.css.prefixes.transforms", true);
 pref("layout.css.prefixes.transitions", true);
 pref("layout.css.prefixes.animations", true);
 
+// Is support for the :scope selector enabled?
+#ifdef RELEASE_BUILD
+pref("layout.css.scope-pseudo.enabled", false);
+#else
+pref("layout.css.scope-pseudo.enabled", true);
+#endif
+
 // pref for which side vertical scrollbars should be on
 // 0 = end-side in UI direction
 // 1 = end-side in document/content direction