I guess nobody's monitoring this forum.

Is the "Restore Previous Session" item grayed (disabled) ?

Make sure you do not run Firefox in permanent Private Browsing mode (Always use Private Browsing mode; Never Remember History).

• https://support.mozilla.org/en-US/kb/private-browsing-use-firefox-without-history
• https://support.mozilla.org/en-US/kb/common-myths-about-private-browsing

• Options/Preferences -> Privacy & Security
  Firefox will: "Use custom settings for history"
• remove checkmark: [ ] "Always use Private Browsing mode"

You can check for problems with the sessionstore.jsonlz4 file in the Firefox profile folder that stores session data.

• delete sessionstore.jsonlz4 and sessionstore.js when present

When sessionstore.jsonlz4 is deleted you lose pinned tabs and open tabs and you will have to recreate them, so if necessary make a note or bookmark them.

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

"Restore Previous Session" is not shown at all. I am not using Private Browsing mode. I don't see those 2 "sessionstore" files that you said to delete.

BTW it's the same on all 3 of my PC's. See the attached screenshot.

Note that Firefox won't show "Restore Previous Session" in the menu when you restore the previous session automatically (i.e. the startup setting is "Restore previous session")

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

• do not clear the Browsing History

• Options/Preferences -> 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

• clearing "Site Preferences" clears exceptions for cookies, images, pop-up windows, and software installation and exception for password and other website specific data
• clearing "Cookies" will remove all selected cookies including cookies with an allow exception you may want to keep

After checking the above settings.

Could you check whether your Firefox is updating the session history files during your session? You can peer on those this way:

Open your current Firefox settings (AKA Firefox profile) folder using either

• "3-bar" menu button > "?" Help > Troubleshooting Information
• (menu bar) Help > Troubleshooting Information
• type or paste about:support in the address bar and press Enter

In the first table on the page, on the Profile Folder row, click the "Open Folder" button. This should launch a new window listing various files and folders in Windows Explorer.

Double-click into the sessionstore-backups folder. You should see a pair of files with very recent modification times:

• recovery.jsonlz4 -- updated as often as every 15 seconds when tabs change
• recovery.backlz4 -- updated after a slight lag from recovery.jsonlz4

Is Firefox creating and updating these files as you browse? (You might also find some other files with older data.)

When you are using Restore Previous Session on the Options page, Firefox may retain recovery.jsonlz4 at shutdown, but create a slightly trimmed version (removing extra "back" button history) at the main level of your profile folder under the name sessionstore.jsonlz4.

Both of these files should rest quietly until you start Firefox up again. Beware of "cleaning" software that may touch Firefox files such as Advanced SystemCare or CCleaner. They might monitor for Firefox exiting and scrub history at that time (or only at system startup).

Here are my settings for clearing history. None of these settings have been changed for eons. The 2 files mentioned above do change when browsing. I use CCleaner Free so they should not be cleared automatically. I have 3 Windows 7 systems that all have this problem. I also have a Windows 10 system that will restore the previous session whether the box under Preferences>General>Startup is checked or not and I can find no differences in the settings on that system. All 4 are running FF 74.0. On the 3 W7 PC's, if I close Firefox (red X) with several tabs open I can not restore them when I reopen Firefox. If I uncheck Restore previous session in the settings, then it is shown in the History and 3-bar menus, but it is greyed out. I'm really confused.

Did you already try to disable the "Restore Previous Session" startup setting and have the entry visible in the menu ?

As I said in my last post, Daddyo37 said

If I uncheck Restore previous session in the settings, then it is shown in the History and 3-bar menus, but it is greyed out. I'm really confused.

Daddyo37 said

The 2 files mentioned above do change when browsing.

What happens with recovery.jsonlz4, recovery.baklz4, and/or sessionstore.jsonlz4 (at the main level of the profile folder) when you exit out of Firefox?

The first 2 files you mentioned go away. Did not see the third. Apparently my situation is caused by having more than one Firefox window open, each with multiple tabs, which I normally do. It will restore my previous session properly if I open only one window. I don't think it's always been that way, but I guess I can live with it. I will just have to be more cautious when I close a Firefox session.

Hi Daddyo37, by default, Firefox can re-open the last 3* closed windows. There are a few different ways to do that after session restore (or during your running session). Either:

• "3-bar" menu button > Library > History > Recently Closed Windows
• "Library" toolbar button > History > Recently Closed Windows
• (menu bar) History > Recently Closed Windows
• Ctrl+Shift+n

To avoid getting in a situation where an important window is considered close, exit Firefox using the menu instead of using "X" on individual windows. Either:

• "3-bar" menu button > Exit
• (menu bar) File > Exit
• (keyboard) Alt+F then x

* If you need more than 3, there is a preference for that. I set browser.sessionstore.max_windows_undo to 10 myself. See: Configuration Editor for Firefox.

Good tips! Thank you very much.