Features
- firestore, count: implement AggregateQuery count() on collections (bd52301)
Bug Fixes
- auth, emulator: guard against double useEmulator calls (13402d5)
- database, useEmulator: drop multiple calls to useEmulator (5fcfc44), closes #5650
- firestore, emulator: avoid double calls to useEmulator (4e0d188), closes #5723
- storage, emulator: avoid calling useEmulator multiple times (276630d), closes #5860