Check in about:config if browser.sessionstore.max_resumed_crashes has 0 value, if it is 0 you must modify to 1.

see: Browser.sessionstore.max resumed crashes

see also: Session Restore

thank you

Please mark "Solved" the answer that really solve the problem, to help others with a similar problem.

It is possible that there is a problem with the files sessionstore.js and sessionstore.bak in the Firefox Profile Folder.

Delete the sessionstore.js file and possible sessionstore-##.js files with a number and sessionstore.bak in the Firefox Profile Folder.

• Help > Troubleshooting Information > Profile Directory: Open Containing Folder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

Deleting sessionstore.js will cause App Tabs and Tab Groups and open and closed (undo) tabs to get lost, so you will have to create them again (make a note or bookmark them).

See also:

• http://kb.mozillazine.org/Session_Restore
• http://kb.mozillazine.org/sessionstore.js
• http://kb.mozillazine.org/Multiple_profile_files_created

Okay???

Which of these two answers is better for solving this?

And (developers) why do I have to make any changes at all? Restore worked fine from update to update until v10.