Hi Robert, is your Firefox set to automatically restore your previous session? There is a checkbox for that on the Settings page. In fact, it's the first option:

I decided to use this option after one too many software updates led to a page popping up in Firefox while it was closed, and me snapping it shut immediately, forgetting that this would replace my huge previous session history with a one-tab previous session history. (Sad face/Angry face/etc.)

If Firefox may already have restored your session -- this would be a good reason that Restore Previous Session would be missing from the History menu -- look for one of these to recover a window that was closed before your last shutdown:

• "3-bar" menu button > History > Recently Closed Windows
• (menu bar) History > Recently Closed Windows
• optional "Library" toolbar button > History > Recently Closed Windows

If it's not there either, hmm, does your computer have any cleaning tools installed that remove browser history from time to time?

Use one of these to close Firefox if you are currently doing that by clicking the close X on the Firefox Title bar, especially if you have multiple windows open to prevent losing tabs in unnoticed windows.

• "3-bar" menu button -> Exit (Power button)
• Windows: File -> Exit
• Mac: Firefox -> Quit Firefox
• Linux: File -> Quit

Thank you. And "Yes": Firefox is set to Open Previous windows and tabs. It's been that way for years. But as we all know, sometimes settings get changed when we not looking. :-)

> If it's not there either, hmm, does your computer have any cleaning tools installed that remove browser history >from time to time?

No software cleaning tools that I'm aware of. I run a pretty basic system.

This problem (losing previous tabs), after closing down gracefully, has occurred more than I'd like (say 2% of the time) over a period of ~5+ years. Firefox is up to date.

Still seems to me that keeping a history of Tabs (like Firefox keeps a browsing history) would be beneficial.

Thanks again for you response.