Well if you personally haven't downloaded/installed any 'ADD-ons' then there is every likelihood you may not have any. These add-ons are designed to give additional functions to your browser.
So add-ons by their nature have to be added by the user. There are however some exceptions, the Avast Online Security (AOS) add-on, which on a default installation of avast (Browser Protection option) would install the AOS add-on. But since the Browser Cleanup is an avast function/tool (which I haven't installed), I don't know if it would report the avast AOS add-on.