When I run my swift 3.2 code with Xcode 9 beta 4 this is the error I get:
*** Terminating app due to uncaught exception \'com.firebase.core\', reason: \'[FIRAp
delete any other "GoogleService-Info.plist" files that have been previously installed. in my case, when I installed it, it was names as "GoogleService-Info.plist-2" since I had another file installed in the same folder. it looks that this will create a confusion for firebase. I deleted all old files and changed the name of the current one to "GoogleService-Info.plist" exactly. it worked.