[CRITICAL] Signup doesn't complete via Firefox private browsing

[dandv]

1. Visit the demo
2. Click the LOGIN button, then the Sign up tab in the Auth0 interstitial
3. Sign up with email/password

The flow gets stuck at the callback spinner screen.

The URL was

https://gatsby-theme-auth0.netlify.app/auth/callback/#access_token=doJmVJcxDrx4bgF91KLT9z5nmM2KDyjf&scope=openid%20profile%20email&expires_in=7200&token_type=Bearer&state=gmvYombuZXQS71aXSSlpavXEgZmQmVzV&id_token=eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCIsImtpZCI6Ik5UbERSakV4TmpCQ01VWTFORU16TUVZeFJUTTVRa000TmpReE5VTkNSVE13UmpGRU1qSXdNZyJ9.eyJuaWNrbmFtZSI6ImRkYXNjYWxlc2N1K2dhdHNieXRoZW1lYXV0aDAiLCJuYW1lIjoiZGRhc2NhbGVzY3UrZ2F0c2J5dGhlbWVhdXRoMEBnbWFpbC5jb20iLCJwaWN0dXJlIjoiaHR0cHM6Ly9zLmdyYXZhdGFyLmNvbS9hdmF0YXIvMmU2NjNlYWEzYjhmZTJiYzgwOTczNjQxYTA4MTQxYWU_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.bcCrNNKHp1b_xod6Epn_DFo3QUEnMkIidZ6J9_GV46oIwN12UDX_bqXU75rtA8V3tEsz2gNiEx5hS4r8JI6_oIMWBQUT4v7Fl90luvRgdhnruaCxEtJfQyE_S1lIqq5JKSa504gDZQ1N8gN_TgNvpfCii1Ejadwr6plyW-edcgXSWiThprmdZJJ-JKu154_1Gh8_75rx7Yrn6TQPj9ob5IhK6XUOhbSpv6XjCzcwm1maB4dWyan5uEbnHII_QuBfEGq7u_pkV1wcRGmKQSSQpF4L5lElEvk__IrGhGRxsKPoq5ebgDZxD1S36gFHKBt4GOO07RCy9WJO-gwaq17FNw

Reproduced with Firefox on Windows 10, Ubuntu 20 and Mac OS 10.15.5.

[jacobcarrington]

Sounds similar to an issue i had, see: https://github.com/epilande/gatsby-theme-auth0/issues/217