Cant' install chrome web store extension in private mode - Fails with access denied after downloading .crx file

[moritzhaller]

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Description

• Custom developed extension fails to install if uploaded to chrome web store in private mode
• The extension installs as expected in Chrome but fails to install in Brave
• When clicking the "Add to Brave" button, the installation fails with the error "An error has occurred -Access denied" after downloading a .crx file (see screenshot below)

Steps to Reproduce

1. Open Brave
2. Ask @moritzhaller to whitelist you as test user for the extension
3. Visit extension website in chrome web store
4. Click "Add to Brave"
5. Error should occur

Actual result:

Expected result:

Successfully installed extension

Reproduces how often:

Easily reproduced on two personal laptops (both Macbook pro/Mojave)

Brave version (brave://version info)

Brave | 0.70.122 Chromium: 78.0.3904.87 (Official Build) (64-bit)
Revision | 20c21f4010010f32462ea8e1d6af30cef66d48c8-refs/branch-heads/3904@{#840}
OS | macOS Version 10.14.6 (Build 18G95)

Version/Channel Information:

• Can you reproduce this issue with the current release? Yes
• Can you reproduce this issue with the beta channel? Didn't test
• Can you reproduce this issue with the dev channel? Didn't test
• Can you reproduce this issue with the nightly channel? Didn't test

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields? No
• Does the issue resolve itself when disabling Brave Rewards? No
• Is the issue reproducible on the latest version of Chrome? No

[rebron]

blocked on #7167

[jantimon]

I have the same behaviour even if I am not using private mode.

Brave Version 1.2.42 Chromium: 79.0.3945.117 (Official Build) (64-bit)

After allowing third party cookies I was able to install the extension:

[flowli]

@jantimon Same behaviour here with exact same Brave/Chromium on macOS.