brave-browser: [Desktop] Can't sign in with firebase website with shields up

Description

We use Firebase for sign in with GitHub on EricElliottJS.com. I’m unable to sign in with shields up in Brave. It works great with shields down.

Steps to Reproduce

1. Go to EricElliottJS.com and click “sign in” in the upper right hand corner.
2. Make sure you have shields up.
3. Click “Sign In with GitHub”

Actual result:

Sign in fails and an error object is logged to the console:

{
  code: "auth/web-storage-unsupported",
  message: "This browser is not supported or 3rd party cookies and data may be disabled."
}

Expected result:

Delegated authentication is a common way to improve security and user privacy by reducing the available attack surface for nefarious collectors of usernames and passwords. I hope we can figure out how to enable commonly used authentication methods and still protect user privacy.

Reproduces how often:

Easily reproduced.

Brave version (brave://version info)

0.65.120 Chromium: 75.0.3770.90 (Official Build) (64-bit)

Revision | a6dcaf7e3ec6f70a194cc25e8149475c6590e025-refs/branch-heads/3770@{#1003} OS | Mac OS X

Version/Channel Information:

Don’t know. Don’t have time to check.

• Can you reproduce this issue with the current release?
• Can you reproduce this issue with the beta channel?
• Can you reproduce this issue with the dev channel?
• Can you reproduce this issue with the nightly channel?

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields? Yes.

• Does the issue resolve itself when disabling Brave Rewards? Don’t know.

• Is the issue reproducible on the latest version of Chrome? No.

Miscellaneous Information:

P.S. Using Brave as my default browser. Looking good. I have high hopes for the future of Brave and the BAT ecosystem.