Note that it still won't warn you if you have the "Warn you when closing multiple tabs" options unchecked. Source: https://bugzilla.mozilla.org/show_bug.cgi?id

Note that it still won't warn you if you have the "Warn you when closing multiple tabs" options unchecked. Source: https://bugzilla.mozilla.org/show_bug.cgi?id=502908#c68 https://bugzilla.mozilla.org/show_bug.cgi?id=502908#c68 > We don't intend to add a third, separate pref/warning for people who do want to have a quit warning, don't turn on session restore, and don't want warnings when closing windows / multiple tabs (ie making browser.tabs.warnOnClose = false + no automatic session restore + browser.warnOnQuit = true show a dialog is not something we're interested in doing.