I had Fast Close Tabs addon for Firefox 56 but it does not work in newer FF versions. The addon changed FF's window close button behaviour so that when pressing the window close button only the current tab was closed. This was very convenient and fast way to close a tab because it did not require careful mouse aiming (when window is maximized) or keyboard shortcut. Just move mouse pointer to top right corner of the screen and click. My understanding is that it is not possible to do similar addons anymore. But I was wondering is it possible to get similar behaviour by using firefox autoconfig file? There are two events that I have found: - quit-application-requested - browser-lastwindow-close-requested I don't know which one is the correct one and how to change it's behaviour. I guess I must use Services.obs.removeObserver method but no idea how.