When you have like 2 windows opened where 1st is your main one and the other one was opened with ctrl+n if you then close the main one and the child one after and restart the browser it will show you the tabs belonged to the child one. Maybe that would be a good idea to toggle some setting which will save the 1st opened window as the main one for the current session. So if you do that you will see the main one after restarting if this setting is enabled.