Firefox can restore all windows and tabs that were open when it was last closed or terminated unexpectedly. This article describes the circumstances under which Firefox will restore your previous session and how you can configure it.
If you had tabs and windows open when you last closed Firefox, the default Firefox home page will have a Restore Previous Session button on it. To get your tabs and windows back, just click it.
Here's how to get your tabs and windows from a previous session back if you don't use the default Firefox home page:
When a new extension or theme is installed, you must restart Firefox to enable the new add-on. To restart, click Restart Now. All windows and tabs are re-opened when Firefox restarts and installs the new add-on.
To apply any updates to the Firefox application that have been downloaded, you must restart Firefox. To restart, click Restart Firefox to Update.
When you restart with add-ons disabled to troubleshoot Firefox problems, your tabs and windows will be reopened.
Due to unexpected issues such as problems with a website, software errors, or an accidental loss of power, Firefox may unexpectedly close. In these situations, Firefox can restore the pages that you were visiting when it is restarted. Firefox will automatically restore your previous session, the first time you launch it after a crash.
If Firefox crashes a second time, the Restore Session (i.e. "Well, this is embarrassing") page will appear when you next launch Firefox.
You can set Firefox to always show your windows and tabs from your previous session each time you start Firefox. To change your Firefox startup settings, see Configuring session restore, below.
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:
Session Restore may keep you logged in to sites that you were logged in to before you closed Firefox. If someone else used your computer after you, they could access your account on these sites. If this is a concern then you should not configure Firefox to open all windows and tabs from your previous session.
You may also wish to disable the Session Restore crash recovery feature which is enabled by default. This will prevent restoring a previous session when Firefox is opened after an unexpected close or software crash:
In the address bar, type about:config and press EnterReturn.
To get your tabs and windows back from a previous session, you should close Firefox from the menu: Click the menu button and then click ExitQuit . If you close each window or tab, only the tabs in the final window that you close are available when you restart Firefox.
For other session restore problems, you may need to make corrections to your Firefox settings:
Based on information from Session Restore (mozillaZine KB)