Unfortunately, Webextension API on Firefox does not currently have the capability to detect/use internal browser's cookie manager.

Webextensions do not have the capability to detect saved logins, so all sites must be manually configured in settings or during browsing through the toolbar icon. This is not a limitation of this webextension but Firefox's Webextension API.

If you would like some help with configuration, please head over to our GitHub repository for support through the discussions area.