Save each window as a separate session, automatically.
If you often have many windows open and you wish you could close some of them without losing any of their tabs, you've found the right extension.
Each window can be saved as a separate session, any change to the tabs will be saved automatically, so that you can close any window at any time, and re-open it back with just 2 clicks.
Sessions can be renamed and removed.
If the current window is a saved session a counter displaying the number of opened tabs in it will be shown.