No, you aren't forced to open the popup, although you are strongly encouraged. I find it easy to ignore a little yellow light on the top bar because I'm not usually even looking at the top bar unless I'm reading messages. The little message underneath the shopping cart (Decorez vos pieces...) is harder to ignore, so I usually open the popup if I get one of those.
When I do choose to open the popup, I usually close it immediately by pressing ESC right after I click on the basket. Takes about 1 second. After that, even the little yellow light is gone. The light doesn't come back until the next time I load the game from the desktop.
As I said, it's very easy for me to ignore. It only takes me a few seconds, at most, each time I start from the desktop. I wish the loading screens were that short.
Even a minor annoyance is to much. I didn't pay hundreds to look at ads but to play, period.
