"Requires" very suspicious optional permissions it will prompt you for such as accessing data for all websites. It works perfectly fine without the permission so I worry it is selling information.
You can find the extension's source code at https://github.com/AudDMusic/firefox-extension.
On many streaming websites, the audio source is in an iframe/embedded content, which the extension can't access to record audio without that permission.
The only information the extension sends us is information about the current tab when the add-on is opened and the corresponding recorded audio.
