Bug 1102898 - Need to unregister plugin offline observer on Mac, Linux (r=bsmedberg)

dom/plugins/ipc/PluginModuleParent.cpp

@@ -289,14 +289,14 @@ PluginModuleChromeParent::~PluginModuleChromeParent()
         UnregisterInjectorCallback(mFlashProcess2);
 #endif
 
+    UnregisterSettingsCallbacks();
+
     Preferences::UnregisterCallback(TimeoutChanged, kChildTimeoutPref, this);
     Preferences::UnregisterCallback(TimeoutChanged, kParentTimeoutPref, this);
 #ifdef XP_WIN
     Preferences::UnregisterCallback(TimeoutChanged, kHangUITimeoutPref, this);
     Preferences::UnregisterCallback(TimeoutChanged, kHangUIMinDisplayPref, this);
 
-    UnregisterSettingsCallbacks();
-
     if (mHangUIParent) {
         delete mHangUIParent;
         mHangUIParent = nullptr;