Works in 2020.

If you have backup of your user data, then there should be file:

sessionstore-backups/recovery.jsonlz4
or
sessionstore.jsonlz4

in your profile. Where is profile?

WIndows:
C:\Users\You\AppData\Roaming\Mozilla\firefox\Profi les\your.profile-1234\

Linux: /home/You/.mozilla/firefox/your.profile-1234/

After closing destination Firefox browser, copy most up to date above mentioned file from your backuo/working profile to the new profile folder:

and always make it named (rename if needed) as sessionstore.jsonlz4 and palce it into the profile root folder (example: /your.profile-1234/sessionstore.jsonlz4) - backup existing file if you would have to replace.

Start and hopefully your tabs session will be restored.