Firefox 127 update did not restore previous session!

[MeanJim]

I was just prompted that a new update was available, so I updated and restarted.  I had several pinned tabs set up and several other open tabs that were lost after the update, and the recently closed tabs view is empty.

The last time this happened (a very long time ago), there was a sessionstore.js.back or some similar file that I could rename and get the session back, however apparently this has changed.  I see a sessionstore-backups directory with 4 files in it, a recovery.baklz4 and recovery.jsonlz4, both of which are 1KB.  The other two, recovery.baklz4 and upgrade.jsonlz4-20240606181944 are both the same size 280KB, which must be what I need, but how do I get it to restore them?

[MeanJim]

Disregard.  After posting and closing Firefox, it created a sessionstore.jsonlz4 in my profile directory.  I copied the upgrade.jsonlz4-20240606181944 and renamed it sessionstore.jsonlz4 and moved it to the profile, overwriting the file.  Upon starting Firefox, my old session was restored.

[Phoenix_]

Thank you for the solution!
I just rewrite all the instructions, for a newbie like me took some time to understand:

1)open firefox:
type about:support
open the listed "profile folder" (located around row 12)
close firefox !

2)create a backup(a copy) of the file "sessionstore.jsonlz4" somewhere else just in case.
open the subdirectory /sessionstore-backups inside "profile folder"
copy file "upgrade.jsonlz4-20240606181944"
Go one folder up ("profile folder"), paste it and rename to "sessionstore.jsonlz4"

3)open firefox, your previous opened tabs should be restored.