Good and useful addon. Hotkeys are a little bit inconvenient. Could you add some convenience options that ctrl + mouse wheel = zoom in/out and ctrl + mouse drag = move video in that direction? If addon API itself does not allow such hotkeys then maybe you can inject some kind of user script or something? If you don't want to have it by default you could have checkbox on your addon's settings page. That if checked then extra JS is injected to youtube that sets up it's own event listeners that are capable of reacting to these shortcuts.

Edit tnx for updating. Updated my rating also from 4 to 5.