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.

When session restore occurs

When you select Restore Previous Session from the Firefox menu

Here's how to get your tabs and windows from a previous session back using the Firefox menu:

1. Click the menu button on the right side of your toolbar.
2. Click History and then select Restore Previous Session.
   
   

After a Firefox update

To apply any updates to the Firefox application that have been downloaded, you must restart Firefox. To restart, click Restart to update Firefox.

After restarting Firefox in Troubleshoot Mode

When you restart in Troubleshoot Mode to diagnose Firefox problems, your tabs and windows will be reopened.

After a crash

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 page will appear when you next launch Firefox.

• To restore the previous session, select the windows or tabs you want to restore and click Restore Session.
• If Firefox continues to experience errors when windows and tabs are reopened, you can launch Firefox without restoring these items. To start a new session, click Start New Session.

When you've set Firefox to restore the previous session at startup

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.

Configuring session restore

When Firefox starts, a single window is opened by default, displaying your specified home page. If you wish, you can configure Firefox to open the windows and tabs from your previous session:

1. In the Menu bar at the top of the screen, click Firefox and then select Preferences or Settings, depending on your macOS version.Click the menu button and select Settings.
2. Select the General panel.
3. Below Startup select Open previous windows and tabs
   .
4. Close the Settings page. Any changes you've made will automatically be saved.

Privacy issues

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:

1. Type about:config in the address bar and press EnterReturn.
   A warning page may appear. Click Accept the Risk and Continue to go to the about:config page.
2. In the Search preference name box at the top type browser.sessionstore.resume_from_crash.
3. Click the Toggle button next to browser.sessionstore.resume_from_crash to set it to false.

Troubleshooting

Previous session not correctly closed

To get your tabs and windows back from a previous session, you should close Firefox from the menu: Click the Firefox menu and select Exit.Click the Firefox menu at the top of the screen and select Quit Firefox.Click the Firefox menu and select Quit. If you close each window or tab, only the tabs in the final window that you close are available when you restart Firefox.

Settings may be incorrect

For other session restore problems, you may need to make corrections to your Firefox settings:

1. In the Menu bar at the top of the screen, click Firefox and then select Preferences or Settings, depending on your macOS version.Click the menu button and select Settings.
2. Select the Privacy & Security panel.
3. In the History section make sure that the Firefox will drop-down menu is set to either Remember history or Use custom settings for history.
   • If Firefox will is set to Use custom settings for history, then make sure that Always use Private Browsing mode is not checked.
   • If Firefox will is set to Use custom settings for history and Clear history when Firefox closes is checked, then click the Settings button and make sure that Browsing & download history is not checked.
4. Close the Settings page. Any changes you've made will automatically be saved.

Based on information from Session Restore (mozillaZine KB)