Open Media Viewer manually by adding in URL next string: "#/media/File:AnyImgFromCurPg.ext
", where "AnyImgFromCurPg.ext
" is an any image from current/active page. For example, the full URL may view something like this: "https://en.wikipedia.org/wiki/Main_Page#/media/File:Foo.jpg
". After pressing Enter key will open Media Viewer with specified image. In Media Viewer press on gear in top right corner and press blue button "Enable Media Viewer".