Multiple firefox windows open, only last one closed asks to save tabs.
I was able to change the setting in about:config to ask to save on close, however; If there are multiple firefox windows open, each one with multiple tabs, only the last window that is being closed will ask to save the tabs.
Wšě wotmołwy (1)
Use "File > Exit" or "Firefox > Exit" if you want to restore multiple windows.
Firefox 4 saves the previous session automatically, so there is no longer need for the dialog asking if you want to save the current session. You can use "Firefox > History > Restore Previous Session" to get the previous session at any time. There is also a "Restore Previous Session" button on the default about:home Home page.