Previous windows and tabs at startup, and history
On my 2020 iMac I have my firefox settings set to open previous windows and tabs at startup. If I close firefox and then reopen it, particularly after startup, the previous windows and tabs are gone. Usually I can open history and restore the previous windows and tabs. Today, for the first time, at startup, not only were the previous sessions' windows and tabs gone, but there was no history of any sort. I did not clear the history, but all my history is gone.
How do I get firefox to reliably reopen my previous windows and tabs, and now, how do I retrieve all my history?
Make sure you are not using Private Windows (nothing is recorded).
You may have corrupt sessionstore [v56] sessionstore.jsonlz4 file(s). Delete all sessionstore* files and the sessionstore-backups folder.
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
Type about:support<enter> in the address box.
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.