Rated 4 out of 5 stars
Is it possible to make it so that you can hold 'ctrl' and click the fullscreenbutton and it goes to fullpage or the other way around?
I think you mean to ask if it's possible to modify the behavior of the 'built-in' fullscreen buttons in videos. This is unfortunately not possible, as I have no control over external code (flash etc.). I might be able to pull it off for HTML5 video... I'll look into that. For now, if you mislike the TabCinema button popping up next to videos, please look at the options menu (Firefox button > Add-ons > TabCinema) to change if and when these buttons should pop up :-)