Up until Firefox v3.6, closing a window with multiple tabs open, a query asking to Save the tabs was shown. In Firefox 4.0 this isn’t the case. I found this feature quite useful. Getting this back is quite simple. This is what needs to be done.
1. Open a tab or a window and type
2. In the resulting window, search for each of the following in the filter bar:
browser.warnOnRestart, browser.warnOnQuit, browser.tabs.warnOnClose, browser.showQuitWarning.
3. Toggle the values of all the above to
That’s it. Now on closing the window the familiar popup is shown.