This come if you want to sign in to mozilla websites:
The persona.org service is shutting down. This service will be unavailable after November 30th, 2016. More Info...
Because, I used google account, the process of sign in will try to access your google account using oauth2 authentication process.
OAuth 2.0 is the next evolution of the OAuth protocol which was
originally created in late 2006. OAuth 2.0 focuses on client developer
simplicity while providing specific authorization flows for web
applications, desktop applications, mobile phones, and living room