FCM service worker error

[thegobot]

In Firefox 49.0.1, after messaging.requestPermission()

Requesting permission...messaging:221:5
Notification permission granted.messaging:225:7
service workerfirebase-messaging-sw.js:1:1
Service worker event waitUntil() was passed a promise that rejected with 'TypeError: b is null'.firebase-messaging.js:21:1
Sending token to server...

[gauntface]

I just remembered, I think this was an error I was hitting in Firefox due to a race condition with updating. (cc @wanderview).

This should be fixed in 3.5.1 of the Firebase SDK.