I feel your pain, I've lost 40+ tabs and was not happy! ;-(( Which is why I've started bookmarking open tabs and running multiple versions of Firefox because the Sync process views the different versions as separate devices. I make sure that the different versions can see the other versions tabs under the Synced Tabs. When I lost tabs in Nightly after an update, I was able to go into another version of Firefox and send the tabs to Nightly. see screenshots

You may have corrupt sessionstore [v56] sessionstore.jsonlz4 file(s). Delete all sessionstore* files and the sessionstore-backups folder.

Type about:support<enter> in the address bar.

Under the page logo on the left side, you will see Application Basics. Under this find Profile Folder. To its right press the button Show Folder. This will open your file browser to the current Firefox profile. Now Close Firefox.

Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder

Linux: Under the page logo on the left side, you will see Application Basics. Under this find Profile Directory. To its right press the button Open Directory.

Locate the above file. Then rename or delete it. Restart Firefox.

Don't delete the files if you need to rescue any data from them, just move them out of the profile folder to some location where Firefox doesn't look for them. You can try to read out their contents using this tool: https://www.jeffersonscher.com/res/scrounger.html

Thank you gentlemen for trying to help me but I am a 70 years old geezer that does NOT have a clue about what you are talking about.

Can you please clarify (pretend you are talking to 5 years old) what you are trying to describe?

And give me step by step instructions on how to restore my tabs?

Thanks a lot.

Mr. Alain Braux

What is it you want to do?

Hello Fred

Due to what seems to be an update, I lost all my tabs and Firefox would not allow me to restore them.

Alain

I used to have this problem until I discovered a setting at the top of the General settings page. Under the Startup section, check the 'Restore previous session' check box. It won't get the tabs that you lost back, but going forward, Firefox will remember what tabs you had open the last time you used it. (For the life of me, I don't know why it comes out of the box unchecked.)

Thank you Rah for this simple and effective solution to my problem. Like you, I don't understand why it isn't set up checked to start with. Firefox used to remind us to restore, then it did it automatically until last week. Then no restore and no explanations as to why or how to fix that issue. Thanks again. Alain

thank you for the answers - changing the setting did not do a thing for the upgrade/lost tabs, it only helps going forward, not back firefox seriously dropped the ball on this one