I have HTC Gratia. It is not rooted. Android version 2.2. So here is the whole story. I stopped receiving notifications from Facebook Messenger app when somebody messages me on Facebook. I used to have this problem before when the app updated to the new version. But when that happened I fixed it by Clearing the app data and logging in again. Since back than I had no problems with notifications and messages. For 1 week I noticed that I don't receive notifications again. I tried again to clear the data and logging in again, it did not work. I uninstalled the app and installed it again and I still don't get notifications. Now I have to open the app everytime in order to check if somebody has messaged me.