I think that when "open last pages on start" is enabled in settings, firefox however should not open at start last closed single tab, if it was closed by clicking on 'close tab' button. Because now there is no way to close this last tab easily in such a way, that it would not be opened after restarting firefox. I think that firefox should open last closed tab at start only if the tab itself was not closed, but firefox was closed by closing entire last window. In other words, it would be good to provide ability to reopen last tabs after restarting firefox, but also provide ability to close all them when you want in such a way, that firefox would not open them again (and just will open start page or blank page). Of course it can be done by opening manually start page or blank page and then closing other tabs, and then closing this new tab too, but it's complicated a bit.