I see, the pop up window does not show any sign-in form, but facebook has a sign-in form.
I think it is the configuration of the google sign-in, not from firebase.
Firebase will always "Stay Signed In", you might try these steps -
1. try login once in that test capx, then close the window.
2. disable the "condition: on start of layout", then run it again.
3. the log will still show "Is Login..", however, user does not run any login action in this case.