Permanently closing App’s “New Window”

There are many articles describing how to close instances of an App(New Window) but my issue is with my IPad remembering the closed window and bringing it back when requesting a new window. It is useful to save multiple app instances and being able to restore them using “Reopen Closed Window” but I would like to close the ones I don’t need anymore.

In my case I have multiple Firefox windows opened by mistake, which I would like to delete permanently instead of collecting them. The same behavior can be observed for Safari too.