If an user comes from Windows based software, where in forms you navigate through the inputs with enter key and save by ctrl+s, to browser based software where the default navigation is done with the tab key and save with enter, what can I assume about user's mental model?
If it's a power user who has filled Windows based forms rapidly with only keyboard, and to put it extreme, with only number keys where you can type in a number, hit enter, type in a number, hit enter, et cetera.. should we assume the user expects same kind of behavior in the browser or should we assume he/she uses the browser software as he/she has learnt to use in other browser based forms (as in, navigate with tab and submit with enter)?
Power user functions, keyboard shortcuts etc are a great add-on to a browser software, but when it conflicts with the default way of the browser handling keyboard events, I think it is quite dangerous and too glitch-friendly code (with few exceptions such as word processing software like Google Docs.. but the main point is to think about form based software).
Thus I find myself in a dilemma and I need different views.
In browser based application, we do use 'tab' to navigate to the next control, but we don't use 'Ctrl+s' to save online forms.
In general, most users expect the same behavior in browser based applications what they do in desktop applications. For instance, I recall one of my user-test sessions on a similar application and I observed users using 'Ctrl+s' after writing a para in Google Docs, which resulted in unnecessary interruptions by web-page-save dialog. Hence, we should try to keep the keyboard events consistent with the platform(based on the %age of users) conventions rather than creating new and contradictory ones.
For entirely new interactions we can also think of defining keyboard shortcuts for power users. More importantly, the guide to the key-shortcuts should be easy to be searched and navigate to. One such example is noteflight.com - https://www.noteflight.com/demo.