In case you use "Clear history when Firefox closes".

• do not clear the "Browsing history"

• Settings -> Privacy & Security
  Firefox will: "Use custom settings for history":
  [X] "Clear history when Firefox closes" -> Settings
• https://support.mozilla.org/en-US/kb/delete-browsing-search-download-history-firefox

• using "Clear history when Firefox closes" in Firefox 102+ honors exceptions and keeps cookies with an allow exception, previous versions removed all cookies
• clearing "Site settings" clears exceptions for cookies, images, pop-up windows, and software installation and exceptions for passwords and other website specific data

See also:

• https://support.mozilla.org/en-US/kb/restore-previous-session

Thank you cor-el

I tried all of the possible settings options and more and it didn't help.

However I have discovered that if I simply close the Firefox window by clicking on the X in the top right corner of Windows then I lose my tabs. If I close Firefox using File/Exit (Ctrl+Shift+Q) or via the 'hamburger' and Exit, then they are retained.

This is either a bug or it is deliberate. If it's deliberate then I don't understand why it would want to work that way when the 'settings' are clearly asking to save tabs when closing Firefox and because the 'confirm close' dialog comes up regardless of which way I use to close Firefox. So it is clear that Firefox knows that I wish to close it in all cases but does not save my tabs if I close the window and not the app itself.

Or am I missing something?

It is possible that you have more than one window open and if you use the close X then only the last closed window will be restored and using Quit/Exit to close Firefox has always been the safest way to close Firefox.

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

Thanks cor-el

I don't have more than one 'window' of Firefox open at any time, but with 4 tabs currently open if I then run Windows Task Manager I can see there are at least 17 Firefox entries showing in the 'Processes' tab using ~1GByte of memory !

Interestingly if I close Firefox with the X in the top right corner there are still 9 entries in the Processes tab. If I use the File / Exit then there are no entries remaining.

If I shut down the computer with Firefox still open it will resume correctly with the previously open tabs still open. But if I close Firefox with the X in the top right corner then I lose all the tabs.

Seems to me like there is some issue in the Firefox code because this was not an issue in the recent past as far as I know.

In any case, I will use the proper exit process in the future to avoid the problem.

Thanks for your assistance.

It is quite normal to see more Firefox processes running.

• process for the main Firefox thread (user interface)
• one or more content processes
  you see more content processes when Fission is enabled
• process for the compositor thread
• process for extensions
• process for WebRender when this feature is enabled

There are several toolkit.aboutProcesses prefs on the about:config page to show more info. You can find the current multi-process state on the Troubleshooting Information page (about:support).

• "Help -> Troubleshooting Information"
  "Application Basics":<be>Multiprocess Windows and Fission Windows
  "Remote Processes" (Web Content)

You can check the about:memory and about:processes pages for info about all processes. See also the about:unloads page for info about the tabs.

Thanks cor-el