Custom URL matching is really nice and works well but the torrents only get added to qBittorrent when I disable authentication. Seems like Torrent Control can't login despite having the correct username and password. I don't get any errors so I can't be sure if that is actually the case or not. All I know is that when authentication is enabled it stops working.
Sadly, this makes this Extension useless to me.

Edit: For some reason https was checked in the qbittorrent webui options. After unckecking https it worked.