[Tested on Firefox 4,5,6,7] This is a short trick to bring back save tabs and quit when you close your Firefox. In Firefox 3, when you have 2 tabs or more and you want to close your Firefox, you'll see notification about saving your tabs. How to enable it in Firefox 4?
1. Open your Firefox and type about:config in Firefox address bar and of course I'll be careful, I promise!
2. Go to the filter box and type quitwarning and it'll show something like this
browser.showQuitWarning
3. Right click on this item and choose toggle. Set the value from false to true.
That's all guys. Try it now :)
