Comment 106 for bug 230102

Of course. As I said, this is because if browser.startup.page = 3 you'll not be informed. And 'A' is an acceptable workaround for now (the only problem is the session will not be saved if you close the last window with only one tab).

@Mike Connor: there's a thing I don't understand in your patch.
If I understood well, if you choice "Do not ask next time" at session saving, browser.tabs.warnOnClose is set to false, instead of browser.warnOnQuit.
But in this way in future you'll not be informed also if multiple tabs will be dismissed when you try to close a window without quitting Fx, or if you select "Close other tabs".