I don't understand what you mean by Facebook emails. Direct messages come through the Messenger app. Any other notifications I receive are in the Facebook app. I don't think that anything opens in Safari.
*edit*
Wait, I think I understand what you mean. Do you mean that you are getting emails from Facebook whenever you have a notification, and tapping the link in those emails takes you to Facebook via Safari?
If so, why not turn off email notifications. Like you said, you must be getting emails every 10 minutes! Just set badge notifications on the app so you can see if there are notifications, and open the app to view them.