I would think that it is the best way for you to delete the Opera app and re install it so that it will clear up the mess. IF you are looking for a download video downloader on Opera's extensions. Then it is at: https://addons.opera.com/en/search/?query=download+video&type=extensions
Off subject, I use the CleanMyMac app to clean it up.
Make sure that your OSX (App Store/Updates) is updated first and then update for all browsers that you have on your computer (or iMac).