The firebase JavaScript library you are using is not compatible with Safari on iOS. The Safari browser running on iOS devices is different from the desktop build of the application and does not have the same set of features.
In this particular case, iOS Safari throws an error in your firebase.js library, trying to use the requestPermission () method of the web notification API to allow firebase to show notifications to the user. The Notification API does not exist though.
You can see the notification API support here: http://caniuse.com/#search=Notification
You may need to look for an alternative or disable the firebase library when your web application is viewed on mobile devices that do not support it. If it should work on iOS Safari, then you should indicate a bug with Firebase and see if there is a patch or update available that fixes the problem in the firebase.js library.
Jeff U.
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