diff --git a/dom/html/nsGenericHTMLFrameElement.cpp b/dom/html/nsGenericHTMLFrameElement.cpp
index 76056536af4d..4b5b71a5965f 100644
--- a/dom/html/nsGenericHTMLFrameElement.cpp
+++ b/dom/html/nsGenericHTMLFrameElement.cpp
@@ -453,18 +453,28 @@ nsGenericHTMLFrameElement::IsHTMLFocusable(bool aWithMouse,
   return false;
 }
 
+static bool sMozBrowserFramesEnabled = false;
+#ifdef DEBUG
+static bool sBoolVarCacheInitialized = false;
+#endif
+
+void
+nsGenericHTMLFrameElement::InitStatics()
+{
+  MOZ_ASSERT(!sBoolVarCacheInitialized);
+  MOZ_ASSERT(NS_IsMainThread());
+  Preferences::AddBoolVarCache(&sMozBrowserFramesEnabled,
+                               "dom.mozBrowserFramesEnabled");
+#ifdef DEBUG
+  sBoolVarCacheInitialized = true;
+#endif
+}
+
+
 bool
 nsGenericHTMLFrameElement::BrowserFramesEnabled()
 {
-  static bool sMozBrowserFramesEnabled = false;
-  static bool sBoolVarCacheInitialized = false;
-
-  if (!sBoolVarCacheInitialized) {
-    sBoolVarCacheInitialized = true;
-    Preferences::AddBoolVarCache(&sMozBrowserFramesEnabled,
-                                 "dom.mozBrowserFramesEnabled");
-  }
-
+  MOZ_ASSERT(sBoolVarCacheInitialized);
   return sMozBrowserFramesEnabled;
 }
 
diff --git a/dom/html/nsGenericHTMLFrameElement.h b/dom/html/nsGenericHTMLFrameElement.h
index 4ab64956228e..fd565e8bb5e8 100644
--- a/dom/html/nsGenericHTMLFrameElement.h
+++ b/dom/html/nsGenericHTMLFrameElement.h
@@ -88,6 +88,7 @@ public:
   void PresetOpenerWindow(mozIDOMWindowProxy* aOpenerWindow,
                           mozilla::ErrorResult& aRv);
 
+  static void InitStatics();
   static bool BrowserFramesEnabled();
 
   /**
diff --git a/dom/ipc/ContentPrefs.cpp b/dom/ipc/ContentPrefs.cpp
index 714c18f76202..6d65b4914cfc 100644
--- a/dom/ipc/ContentPrefs.cpp
+++ b/dom/ipc/ContentPrefs.cpp
@@ -42,6 +42,7 @@ const char* mozilla::dom::ContentPrefs::gInitPrefs[] = {
   "dom.ipc.processPriorityManager.backgroundPerceivableGracePeriodMS",
   "dom.max_chrome_script_run_time",
   "dom.max_script_run_time",
+  "dom.mozBrowserFramesEnabled",
   "dom.performance.enable_notify_performance_timing",
   "dom.performance.enable_user_timing_logging",
   "dom.storage.testing",
diff --git a/layout/build/nsLayoutStatics.cpp b/layout/build/nsLayoutStatics.cpp
index fe8bdc0bd4e2..157a0dc5ae3c 100644
--- a/layout/build/nsLayoutStatics.cpp
+++ b/layout/build/nsLayoutStatics.cpp
@@ -22,6 +22,7 @@
 #include "nsCSSPseudoClasses.h"
 #include "nsCSSPseudoElements.h"
 #include "nsCSSRendering.h"
+#include "nsGenericHTMLFrameElement.h"
 #include "mozilla/dom/Attr.h"
 #include "nsDOMClassInfo.h"
 #include "mozilla/EventListenerManager.h"
@@ -286,6 +287,7 @@ nsLayoutStatics::Initialize()
   nsApplicationCacheService::AppClearDataObserverInit();
 
   HTMLVideoElement::Init();
+  nsGenericHTMLFrameElement::InitStatics();
 
 #ifdef MOZ_XUL
   nsMenuBarListener::InitializeStatics();