Test plan

See #15230

Description

Qwant attempts to use unsupported extension-related APIs, and offers Firefox addons to Brave users.

Steps to Reproduce

Visit https://(www|lite).qwant.com in Brave (Muon). On www… you'll see an extension panel at the top-right of the page. Clicking this will blur the page, causing it to become unusable. On lite… you'll see an addon (for Firefox) offered at the top-right of the page.

Expected result:
Neither should be shown in Brave (Muon)

Reproduces how often:
100%

Reproducible on current live release:
Yes

Additional Information

The extension offering doesn't apply to brave-muon. When the user clicks the [x] to close the panel, www.qwant.com calls ExtensionHelper.closePopin. This creates a key "closedExtPanel" in Local Storage with a value of Date.now().