How to recover from a session crash in Firefox 56 in MacOS

Copypasta'd from a file my mate sent me:

IF FIREFOX FAILS TO LOAD ITS PREVIOUS SESSION AGAIN AND CANNOT RECOVER BY THE HISTORY MENU

FUCKING DO THIS:

1. ~/Library/Application Support/Firefox/Profiles
COPYPASTA DIRECTORY AND ARCHIVE
2. Close Firefox
3. DELETE sessionstore.jsonlz4 in the profile
4. DELETE ALL FILES IN sessionstore-backups
5. COPYPASTA previous.jsonlz4 FROM BACKED UP PROFILE
6. RESTART FIREFOX