Firefox 4 does not ask to save tabs on exit and not display them on restart.

i was using fire fox and it was asking to save all open tabs and after saving them it shows them upon restrating the fire fox , but last week i updated FF to FF4 and this functionality was missing.  then i checked it and came to know how to use this feauter in FF4. here is the way

One change in Firefox 4 is to by default stop Firefox displaying the warning message, but it can be turned back on by changing some preferences.

1. Type about:config into the location bar and press enter


2. Accept the warning message that appears, you will be taken to a list of preferences


3. Locate the preference browser.tabs.warnOnClose, if its value is set to false, double-click on it to change its value to true


4. Repeat this for these 2 preferences browser.warnOnQuit, browser.warnOnRestart


5. Starting with beta 12 there will be an additional preference that needs to be set to true - browser.showQuitWarning

source : http://support.mozilla.com/en-US/questions/786128