@hartkor: And if the extension was obtained from third-party sources and it doesn't work, then you need to switch on developer mode on the extensions page, find its ID in the extension description, go to the Opera profile folder, find there the folder with extensions, find there the folder with this ID, copy it somewhere, just to be sure, and by clicking the "load unpacked" button "install" it from this folder anew (you need to go to the place where the manifest file is). In my case, the extension still has all the same settings as it had.