Have you confirmed you are locked out of Firebase? Performed a password reset?

If you get to login, check your compute resources since most of these bots just deploy tons of compute and use them for DDOS. This can be in the hundreds of dollars per hour figure.

It is possible to have your session hijacked when using any wifi really, its a lot harder on secured wifi though.

I only tether to my phone now in public, and never use unsecured wifi for anything.