diff --git a/dom/bindings/GenerateCSS2PropertiesWebIDL.py b/dom/bindings/GenerateCSS2PropertiesWebIDL.py
index 4be12b72cd1..e1e4a3a56e3 100644
--- a/dom/bindings/GenerateCSS2PropertiesWebIDL.py
+++ b/dom/bindings/GenerateCSS2PropertiesWebIDL.py
@@ -7,9 +7,18 @@ import string
 
 propList = eval(sys.stdin.read())
 props = ""
-for [prop, pref] in propList:
+for [prop, id, flags, pref] in propList:
     extendedAttrs = ["Throws", "TreatNullAs=EmptyString"]
-    if pref is not "":
+    # To limit the overhead of Func= annotations, we only generate them when
+    # necessary, which is when the
+    # CSS_PROPERTY_ALWAYS_ENABLED_IN_CHROME_OR_CERTIFIED_APP flag is set.
+    # Otherwise, we try to get by with just a Pref= annotation or no annotation
+    # at all.
+    if "CSS_PROPERTY_ALWAYS_ENABLED_IN_CHROME_OR_CERTIFIED_APP" in flags:
+        extendedAttrs.append('Func="IsCSSPropertyExposedToJS<eCSSProperty_%s>"' % id)
+    # The following is an 'elif' because it is the responsibility of
+    # IsCSSPropertyExposedToJS to handle the pref if there is one.
+    elif pref is not "":
         extendedAttrs.append('Pref="%s"' % pref)
     if not prop.startswith("Moz"):
         prop = prop[0].lower() + prop[1:]
diff --git a/dom/webidl/CSS2PropertiesProps.h b/dom/webidl/CSS2PropertiesProps.h
index b799db07295..63d5f5eff87 100644
--- a/dom/webidl/CSS2PropertiesProps.h
+++ b/dom/webidl/CSS2PropertiesProps.h
@@ -5,13 +5,16 @@
 
 [
 
-#define DO_PROP(method, pref) \
-  [ #method, pref ],
+#define PROP_STRINGIFY_INTERNAL(X) #X
+#define PROP_STRINGIFY(X) PROP_STRINGIFY_INTERNAL(X)
+
+#define DO_PROP(method, id, flags, pref) \
+  [ #method, #id, PROP_STRINGIFY(flags), pref ],
 #define CSS_PROP(name, id, method, flags, pref, parsevariant, kwtable, \
 		 stylestruct, stylestructofset, animtype) \
-  DO_PROP(method, pref)
+  DO_PROP(method, id, flags, pref)
 #define CSS_PROP_SHORTHAND(name, id, method, flags, pref) \
-  DO_PROP(method, pref)
+  DO_PROP(method, id, flags, pref)
 #define CSS_PROP_PUBLIC_OR_PRIVATE(publicname_, privatename_) publicname_
 #define CSS_PROP_LIST_EXCLUDE_INTERNAL
 
@@ -23,12 +26,14 @@
 #undef CSS_PROP
 
 #define CSS_PROP_ALIAS(name, id, method, pref) \
-  DO_PROP(method, pref)
+  DO_PROP(method, id, 0, pref)
 
 #include "nsCSSPropAliasList.h"
 
 #undef CSS_PROP_ALIAS
 
 #undef DO_PROP
+#undef PROP_STRINGIFY
+#undef PROP_STRINGIFY_INTERNAL
 
 ]
diff --git a/layout/style/nsDOMCSSDeclaration.cpp b/layout/style/nsDOMCSSDeclaration.cpp
index de250c7819d..d438918473e 100644
--- a/layout/style/nsDOMCSSDeclaration.cpp
+++ b/layout/style/nsDOMCSSDeclaration.cpp
@@ -16,6 +16,8 @@
 #include "nsCOMPtr.h"
 #include "mozAutoDocUpdate.h"
 #include "nsIURI.h"
+#include "mozilla/dom/BindingUtils.h"
+#include "nsContentUtils.h"
 
 using namespace mozilla;
 
@@ -429,3 +431,24 @@ nsDOMCSSDeclaration::RemoveCustomProperty(const nsAString& aPropertyName)
   decl->RemoveVariableDeclaration(Substring(aPropertyName, VAR_PREFIX_LENGTH));
   return SetCSSDeclaration(decl);
 }
+
+bool IsCSSPropertyExposedToJS(nsCSSProperty aProperty, JSContext* cx, JSObject* obj)
+{
+  nsCSSProps::EnabledState enabledState = nsCSSProps::eEnabledForAllContent;
+
+  // Optimization: we skip checking properties of the JSContext
+  // in the majority case where the property does not have the
+  // CSS_PROPERTY_ALWAYS_ENABLED_IN_PRIVILEGED_CONTENT flag.
+  bool isEnabledInChromeOrCertifiedApp
+    = nsCSSProps::PropHasFlags(aProperty,
+                               CSS_PROPERTY_ALWAYS_ENABLED_IN_CHROME_OR_CERTIFIED_APP);
+
+  if (isEnabledInChromeOrCertifiedApp) {
+    if (dom::IsInCertifiedApp(cx, obj) ||
+        nsContentUtils::ThreadsafeIsCallerChrome())
+    {
+      enabledState |= nsCSSProps::eEnabledInChromeOrCertifiedApp;
+    }
+  }
+  return nsCSSProps::IsEnabled(aProperty, enabledState);
+}
diff --git a/layout/style/nsDOMCSSDeclaration.h b/layout/style/nsDOMCSSDeclaration.h
index 4ea076716a0..8cb35708aae 100644
--- a/layout/style/nsDOMCSSDeclaration.h
+++ b/layout/style/nsDOMCSSDeclaration.h
@@ -15,6 +15,8 @@
 
 class nsIPrincipal;
 class nsIDocument;
+struct JSContext;
+class JSObject;
 
 namespace mozilla {
 namespace css {
@@ -152,4 +154,12 @@ protected:
   }
 };
 
+bool IsCSSPropertyExposedToJS(nsCSSProperty aProperty, JSContext* cx, JSObject* obj);
+
+template <nsCSSProperty Property>
+MOZ_ALWAYS_INLINE bool IsCSSPropertyExposedToJS(JSContext* cx, JSObject* obj)
+{
+  return IsCSSPropertyExposedToJS(Property, cx, obj);
+}
+
 #endif // nsDOMCSSDeclaration_h___