Hi @Petr.mahdal, The Current UWP App doesn't support the external browser extensions due to unavailability of required APIs to communicate with third party Apps i.e Opera Browser in your case. So to use browser extensions you have to stick with the traditional Windows PC App.
We are also eagerly waiting for the time when Microsoft will support developing extensions for Edge and the corresponding required APIs for UWP Apps to communicate with Edge. Recently they have rolled out couple of Edge extensions only for Insider users https://blogs.windows.com/windowsexperience/2016/03/17/bringing-extensions-to-microsoft-edge/
Hi @Petr.mahdal, The Current UWP App doesn't support the external browser extensions due to unavailability of required APIs to communicate with third party Apps i.e Opera Browser in your case. So to use browser extensions you have to stick with the traditional Windows PC App. We are also eagerly waiting for the time when Microsoft will support developing extensions for Edge and the corresponding required APIs for UWP Apps to communicate with Edge. Recently they have rolled out couple of Edge extensions only for Insider users https://blogs.windows.com/windowsexperience/2016/03/17/bringing-extensions-to-microsoft-edge/