reconnect from different WiFi/unstable WiFi connection not handled very nice (Client side)

[Unip0rn]

What I did:
connected, changed the WiFi I used to connect, used creds I used before changing WiFi
What happened:
just was thrown to the "normal" mode, so where I would be texting, but wasn't able to d anything bc nick was taken
What I expected:
Some sort of recovery, maybe reopening the dialog to set the nick, but also tell to choose another nick.

setup: Firefox 58.0.1 on Linux