Firebase recommended setup on Cordova-Ionic project



I just recently started to develop and Cordova-Ionic app in conjunction with Firebase.
I have one question regarding how to correctly add firebase to the ionic project. Which method is the recommended one.
My app have to work offline meanwhile an internet connection is available.

a) Using firebase CDN files and add the JS files to the index.html (as I required offline mode, maybe this is not the best approach, but not sure)
b) install the firebase libraries via bower (bower install firebase --save)
c) Download the firebase files and add them to the “www/lib” folder and reference them inside the index.html.

I have tried b) and c) and they both seem to work fine, hower I wish to know which approach is the recommended one, or the best practices about this firebase configuration.

For b) I see that bower also download angular related libraries, not sure if this could clash with the ionic default angular libraries.