diff --git a/js/src/jswrapper.h b/js/src/jswrapper.h
index d8cd4a064f9..9e4c1bc8f05 100644
--- a/js/src/jswrapper.h
+++ b/js/src/jswrapper.h
@@ -46,7 +46,7 @@ class JS_FRIEND_API(Wrapper) : public DirectProxyHandler
      * object (via UnwrapObjectChecked) will throw. Otherwise, they will succeed.
      */
     void setSafeToUnwrap(bool safe) { mSafeToUnwrap = safe; }
-    bool isSafeToUnwrap() { return mSafeToUnwrap; }
+    virtual bool isSafeToUnwrap() { return mSafeToUnwrap; }
 
     static JSObject *New(JSContext *cx, JSObject *obj, JSObject *proto,
                          JSObject *parent, Wrapper *handler);
diff --git a/js/xpconnect/wrappers/AccessCheck.cpp b/js/xpconnect/wrappers/AccessCheck.cpp
index a5153a58387..91a3a00311b 100644
--- a/js/xpconnect/wrappers/AccessCheck.cpp
+++ b/js/xpconnect/wrappers/AccessCheck.cpp
@@ -269,6 +269,19 @@ AccessCheck::isScriptAccessOnly(JSContext *cx, JSObject *wrapper)
     return false;
 }
 
+bool
+OnlyIfSubjectIsSystem::isSafeToUnwrap()
+{
+    if (XPCJSRuntime::Get()->XBLScopesEnabled())
+        return false;
+    // It's nasty to use the context stack here, but the alternative is passing cx all
+    // the way down through UnwrapObjectChecked, which we just undid in a 100k patch. :-(
+    JSContext *cx = nsContentUtils::GetCurrentJSContext();
+    if (!cx)
+        return true;
+    return AccessCheck::isSystemOnlyAccessPermitted(cx);
+}
+
 enum Access { READ = (1<<0), WRITE = (1<<1), NO_ACCESS = 0 };
 
 static bool
diff --git a/js/xpconnect/wrappers/AccessCheck.h b/js/xpconnect/wrappers/AccessCheck.h
index dd95e040731..c426a688a93 100644
--- a/js/xpconnect/wrappers/AccessCheck.h
+++ b/js/xpconnect/wrappers/AccessCheck.h
@@ -50,6 +50,9 @@ struct Opaque : public Policy {
     {
         return false;
     }
+    static bool isSafeToUnwrap() {
+        return false;
+    }
 };
 
 // This policy only permits access to the object if the subject can touch
@@ -67,6 +70,8 @@ struct OnlyIfSubjectIsSystem : public Policy {
     {
         return AccessCheck::isSystemOnlyAccessPermitted(cx);
     }
+
+    static bool isSafeToUnwrap();
 };
 
 // This policy only permits access to properties that are safe to be used
@@ -82,6 +87,10 @@ struct CrossOriginAccessiblePropertiesOnly : public Policy {
     {
         return false;
     }
+
+    static bool isSafeToUnwrap() {
+        return false;
+    }
 };
 
 // This policy only permits access to properties if they appear in the
@@ -94,6 +103,10 @@ struct ExposedPropertiesOnly : public Policy {
         return act == js::Wrapper::GET;
     }
     static bool allowNativeCall(JSContext *cx, JS::IsAcceptableThis test, JS::NativeImpl impl);
+
+    static bool isSafeToUnwrap() {
+        return false;
+    }
 };
 
 // Components specific policy
@@ -106,6 +119,10 @@ struct ComponentsObjectPolicy : public Policy {
     static bool allowNativeCall(JSContext *cx, JS::IsAcceptableThis test, JS::NativeImpl impl) {
         return false;
     }
+
+    static bool isSafeToUnwrap() {
+        return false;
+    }
 };
 
 }
diff --git a/js/xpconnect/wrappers/FilteringWrapper.cpp b/js/xpconnect/wrappers/FilteringWrapper.cpp
index d8d06841f92..5ba3b356b2a 100644
--- a/js/xpconnect/wrappers/FilteringWrapper.cpp
+++ b/js/xpconnect/wrappers/FilteringWrapper.cpp
@@ -29,6 +29,13 @@ FilteringWrapper<Base, Policy>::~FilteringWrapper()
 {
 }
 
+template <typename Base, typename Policy>
+bool
+FilteringWrapper<Base, Policy>::isSafeToUnwrap()
+{
+    return Policy::isSafeToUnwrap();
+}
+
 template <typename Policy>
 static bool
 Filter(JSContext *cx, JSObject *wrapper, AutoIdVector &props)
diff --git a/js/xpconnect/wrappers/FilteringWrapper.h b/js/xpconnect/wrappers/FilteringWrapper.h
index b084da30529..c02fc80bb07 100644
--- a/js/xpconnect/wrappers/FilteringWrapper.h
+++ b/js/xpconnect/wrappers/FilteringWrapper.h
@@ -19,6 +19,9 @@ class FilteringWrapper : public Base {
     FilteringWrapper(unsigned flags);
     virtual ~FilteringWrapper();
 
+    // This is potentially dynamic until XBL scopes are no longer behind a pref.
+    virtual bool isSafeToUnwrap();
+
     virtual bool getPropertyDescriptor(JSContext *cx, JSObject *wrapper, jsid id, js::PropertyDescriptor *desc, unsigned flags) MOZ_OVERRIDE;
     virtual bool getOwnPropertyDescriptor(JSContext *cx, JSObject *wrapper, jsid id, js::PropertyDescriptor *desc, unsigned flags) MOZ_OVERRIDE;
     virtual bool getOwnPropertyNames(JSContext *cx, JSObject *wrapper, js::AutoIdVector &props) MOZ_OVERRIDE;
diff --git a/js/xpconnect/wrappers/WrapperFactory.cpp b/js/xpconnect/wrappers/WrapperFactory.cpp
index 057953ed553..ad5f32d1632 100644
--- a/js/xpconnect/wrappers/WrapperFactory.cpp
+++ b/js/xpconnect/wrappers/WrapperFactory.cpp
@@ -284,8 +284,8 @@ DEBUG_CheckUnwrapSafety(JSObject *obj, js::Wrapper *handler,
         // The Components object that is restricted regardless of origin.
         MOZ_ASSERT(!handler->isSafeToUnwrap());
     } else if (AccessCheck::needsSystemOnlyWrapper(obj)) {
-        // SOWs are opaque to everyone but Chrome and XBL scopes.
-        MOZ_ASSERT(handler->isSafeToUnwrap() == nsContentUtils::CanAccessNativeAnon());
+        // SOWs have a dynamic unwrap check, so we can't really say anything useful
+        // about them here :-(
     } else {
         // Otherwise, it should depend on whether the target subsumes the origin.
         MOZ_ASSERT(handler->isSafeToUnwrap() == AccessCheck::subsumes(target, origin));
@@ -499,7 +499,8 @@ WrapperFactory::WrapForSameCompartment(JSContext *cx, JSObject *obj)
 
     // The WN knows what to do.
     JSObject *wrapper = wn->GetSameCompartmentSecurityWrapper(cx);
-    MOZ_ASSERT_IF(wrapper != obj, !Wrapper::wrapperHandler(wrapper)->isSafeToUnwrap());
+    MOZ_ASSERT_IF(wrapper != obj && IsComponentsObject(js::UnwrapObject(obj)),
+                  !Wrapper::wrapperHandler(wrapper)->isSafeToUnwrap());
     return wrapper;
 }