Restore Firefox Tabs On Restart
Some versions of firefox do not ask to save tabs and pages currently open so that they open next time you open the browser.
The following modifications changes that
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 3 preferences: browser.warnOnQuit, browser.warnOnRestart and browser.showQuitWarning
Upon restarting the browser any session open from that point onward, firefox will ask for you to save your tabs/browsing session/open pages for next time