Using "Open Previous Windows and Tabs" in Firefox

Enabling the "Open previous windows and tabs" setting in the Firefox Web Browser allows you to seamlessly resume your browsing sessions right where you left off. This article provides a straightforward breakdown of what happens behind the scenes when you check this box in the General settings, including how Firefox restores your workspace, manages system memory upon startup, handles active logins, and treats private browsing data.

Automatic Session Restoration

The primary function of this setting is automatic session recovery. When you close Firefox and reopen it later, the browser will automatically recreate the exact workspace you had before closing. This includes:

  • All Open Tabs: Every webpage you had open will reappear in the exact order you left them.
  • Multiple Windows: If you had multiple Firefox windows open across different monitors or virtual desktops, Firefox will restore all of them, provided you exited the browser properly.
  • Tab History: Each restored tab retains its specific "Back" and "Forward" navigation history, allowing you to return to previously visited pages within that tab.
  • Scroll Position and Form Data: Firefox remembers how far down the page you were scrolled. In many cases, it will also restore unsubmitted text you typed into web forms or text boxes.

Smart Memory Management (On-Demand Loading)

Restoring dozens of tabs at once could easily overwhelm your computer's memory (RAM) and slow down your internet connection. To prevent this, Firefox uses a technique called "lazy loading" when this setting is enabled.

When you launch Firefox, it only loads the web content for the currently selected, active tab. All other background tabs remain in a suspended state—displaying their titles and icons, but not actually connecting to the internet or using significant RAM until you click on them.

Impact on Cookies and Active Logins

Normally, websites use "session cookies" that are deleted the moment you close your browser, which automatically logs you out of accounts like banks or webmail.

When "Open previous windows and tabs" is enabled, Firefox preserves these session cookies so your tabs can be restored accurately. As a result, you may remain logged into websites that would otherwise log you out when you close the browser. For security, high-risk websites (like financial institutions) will still log you out based on server-side timers, regardless of this setting.

Exceptions to the Rule

Firefox applies specific limitations to this feature to protect your privacy and prevent errors:

  • Private Browsing Windows: Firefox will never save or restore Private Windows or the tabs inside them. Once a Private Window is closed, that session data is permanently erased.
  • Closing Multiple Windows Individually: If you have three Firefox windows open and you close them one by one using the "X" button at the top corner of the screen, Firefox will only restore the very last window you closed. To restore all three windows at once, you must close Firefox by clicking the main application menu (three horizontal lines) and selecting Exit (on Windows/Linux) or Quit (on macOS).