Hm that's indeed the default behaviour if you have NO document open. You then have to press the "create new document" button. There is an option in the preferences to always create a new blank document at startup.

But if you are already working on something, like you said in a previous post, then closing the browser tab leaves you with that document tab open. In fact there is even no need to close the browser tab, just switch between them. Honestly you're the first person ever to complain about that...