How to Configuring session restore in Firefox
By default, when Firefox starts, a single window is opened, displaying your specified home page. If you wish, you can configure Firefox to open all windows and tabs from your previous session:
1. At the top of the Firefox window, click on the Firefox button (Tools menu in Windows XP) and then click Options
2. Select the General panel.
3. From the When Firefox starts drop-down, select Show my windows and tabs from last time.
4. Click OK to close the Options window
Note: Download Firefox (newest version)
See How to Security and passwords settings in Firefox
Via Mozilla