La réponse d'un des dev:
Open up the config file MarvelEngine.ini located here (Documents location can vary based on your Windows install):
SSN: \Documents\My Games\Marvel Heroes Game\MarvelGame\Config\
Steam: \Documents\My Games\Marvel Heroes\MarvelGame\Config\
Look for the line Fullscreen= and make it Fullscreen=False
Save the file, close, and restart the game. Once in game you can go into options and change video settings.