Abrowser by default stops extensions from running on Mozilla domains

Bug experienced on:
abrowser-97.0+build2-0ubuntu0.18.04.1+9.0trisquel85

Steps to reproduce:
* open Abrowser
* configure an extension of choice (LibreJS, uBlockOrigin, NoScript, etc.) to block all/nonfree JavaScript
* visit a page under either of:
* accounts-static.cdn.mozilla.net
* accounts.firefox.com
* addons.cdn.mozilla.net
* addons.mozilla.org
* api.accounts.firefox.com
* content.cdn.mozilla.net
* discovery.addons.mozilla.org
* install.mozilla.org
* oauth.accounts.firefox.com
* profile.accounts.firefox.com
* support.mozilla.org
* sync.services.mozilla.com

Expected behavior:
The extension should block all/nonfree JS on the page as it does on non-Mozilla domains.

Experienced behavior:
(Proprietary) Scripts run happily because Abrowser is stopping WebExtensions from running on those Mozilla domains.

Temporary workaround:
Go to about:config, click through the warning if one appears, loop up `extensions.webextensions.restrictedDomains` preference and set it to an empty string.

This workaround does work but it should not be needed - an ethical user agent should allow the user to use the extensions of choice under any domain.