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I was looking for exactly this feature!

My only comment would be: why not switch the functionality of both buttons? So that the top button closes the entire window and the smaller button below it closes the tab? I would like it even better in that way...

Anyway, good job!

Questa recensione riguarda una versione precedente (1.1) del componente aggiuntivo. 

Close Button should allow you to get the behavior you want.