Bug 541646 - Crash when Flash is running and we enter private browsing mode, r=bent

--HG--
extra : rebase_source : 5f6d75689cf70f6c7bdd578da0021287bfe22737

dom/plugins/PluginInstanceChild.cpp

@@ -358,6 +358,11 @@ bool
 PluginInstanceChild::AnswerNPP_SetValue_NPNVprivateModeBool(const bool& value,
                                                             NPError* result)
 {
+    if (!mPluginIface->setvalue) {
+        *result = NPERR_GENERIC_ERROR;
+        return true;
+    }
+
     // Use `long` instead of NPBool because Flash and other plugins read
     // this as a word-size value instead of the 1-byte NPBool that it is.
     long v = value;