Hi loganj, that's a strange situation.

Are you checking the History menu on the classic menu bar, or the History menu under the new Library button (), or do they both have the same issue of not showing recently closed tabs?

Does Firefox know the actual history -- when you right-click a tab, is Undo Close Tab enabled (not grayed) and if so, does it work? If Firefox has recorded the history but the menu is broken, that would be useful to know, versus Firefox failing to record the history in the first place.

You can file formal but reports on Bugzilla, which is here:

https://bugzilla.mozilla.org/

They may ask if you use any history-related or tab-related add-ons and/or whether you have tested in Firefox's Safe Mode.

For reference, in its Safe Mode, Firefox temporarily deactivates extensions, hardware acceleration, and some other advanced features to help you assess whether these are causing the problem. To try that out:

If Firefox is not running: Hold down the Shift key when starting Firefox.

If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

and OK the restart.

Both scenarios: A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any improvement?

this problem is not always there. It happens from time to time. probably this is 4-5 time that happened. So i have no way to test it. I didn't try to use undo close tab. i forgot completely about that option. And yes both ways showed only tabs from previous session. As for safe mode...i'll never try it again. Last time i've tried safe mode, from 300+ tabs i've lost more than 100 when safe mode started. those tabs were gone even when i start it back in normal mode.

Edit: Undo close tab should restore from last closed tab to first closed tab? cause for me its restoring from 1st closed tab to last closed tab.

Please Refresh but do this 1st:

• https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer
• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

then

• https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-settings

TEST....... If no issues then Extensions which need to be added back in 1 at a time and tested ..... Or it is your Profile : Make a new one and test ...:

• https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

If is your Profile :

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile
• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

Note: Any customization will revert back to default, you will also need to reinstall Extensions.

Please let us know if this solved your issue or if need further assistance.

I notice a Duplicate Tab Closer in the System Details list.

Did you try Safe Mode?

Start Firefox in Safe Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration is causing the problem.

• switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Appearance
• do NOT click the "Refresh Firefox" button on the Safe Mode start window

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

loganj said

Undo close tab should restore from last closed tab to first closed tab? cause for me its restoring from 1st closed tab to last closed tab.

It should be last closed => first opened, yes. It sounds as though something is modifying your session history.