Firefox usually is open because I multitask a lot, same goes for email and other programs at the same time, as said also LDW games.

I do not play fullscreen, that looks terrible. because my screen is flat, all villagers, plants etc. look like they need a diet, but technically I can play also on fullscreen

It probably is due to the screenresolution, mine is at 1280 x 720. try different settings if this does not work