[djsumdog]

I think you can set that in `about:config` without a plugin

[0942v8653]

If you set browser.showQuitWarning to true (also make sure browser.warnOnQuit is true; that should be default) it will show a dialog to confirm if you want to quit. But if you check the box "do not show next time" it will set browser.showQuitWarning to false.