Hi!
Haven't found a similar issue. It is mentioned here: https://issuetracker.unity3d.com/issues/editor-freezes-when-entering-play-mode-and-firebase-getvalueasync-was-used-in-the-last-play-mode
It says unity is not going to fix this. Is this the firebase issue? Will it be resolved? I'm using 2019.2.2 and Firebase 6.4.0 and I have this problem.