In case you use "Clear history when Firefox closes" or otherwise clear history:

• do not clear the Browsing History

• Tools > Options > Privacy > Firefox will: "Use custom settings for history": [X] "Clear history when Firefox closes" > Settings
• https://support.mozilla.org/kb/remove-recent-browsing-search-and-download-history

Make sure that you do not run Firefox in permanent Private Browsing mode (Never remember history).

• https://support.mozilla.org/kb/Private+Browsing

• Tools > Options > Privacy > Firefox will: "Use custom settings for history"
• Deselect: [ ] "Always use Private Browsing mode"

I know I should mark. Save tabs on exit, but nothing works.

Hello,

There was a problem with the hard drive in Windows. After checking disk errors all it worked.