It works more or less as replacement for the old ZoomPage addon, but one thing is missing: It's no longer possible to show large images entirely on the screen. For example this picture
https://upload.wikimedia.org/wikipedia/commons/a/a8/Tour_Eiffel_Wikimedia_Commons.jpg
would need a zoom level below 30% on my screen. There should be a button to automatically chose the correct zoom level so that the complete image is displayed.