Consider this scenario: Jen has a normal window open and a private window open. She's done with the private window but hasn't closed it yet. She starts typing a new Stack Exchange question. Later, she's almost done when she realizes she's not logged in because she accidentally used the private window by mistake. She opens a new question in the normal window, which logs her in automatically. She copies the complete question text, and closes the private window becuase she doesn't need it any more. She hits paste and ... nothing. Two hours of work are gone. She sighs/rages quietly to herself, cursing the stupid computer, and herself for trusting it. ---- It has been proposed elsewhere that "this behavior is expected". https://bugzilla.mozilla.org/show_bug.cgi?id=827260 Who expects an application to behave like this? It violates my mental model of how a clipboard works. The operating system provides a clipboard as a convenience for me to copy data between applications. Once copied to the clipboard, the data exists outside the lifecycle of the source application. Firefox disagrees. It destroys clipboard data without warning or consultation. Please give us an option to turn off this feature.