I have a drawing web app, and I want to use the Alt key to call eyedropper as it works in Photoshop. Everything works well in other browsers, but not in Opera when neither keydown/keypress is invoked when pressing the left Alt key. Other keys are inappropriate for this tool: Shift is already occupied, Ctrl will cause many false triggers, symbolic keys will prevent it from using when a text field is focused, combinations are not convenient for such a usual operation (won't be greeted by the users).
It's really strange to see no answer from developers about this thing which users have been asked for a long time. I understand that you want to keep the Alt key consistency between Windows apps, but no conventions require you to block the entire left Alt key capturing. I think that the keydown event should be captured as it happens in the other browsers, and the menu should be shown only if preventDefault hasn't been called. From the UX perspective, this is the same as preventing opening the default context menu in the apps like Google Docs which you allow to do.
As a developer, I can't think of any existing realization issue preventing you from doing this. At this moment, I have to offer Opera users moving to another browser or using very inconvenient right Alt or a combo for this purpose. Thank you!