Two days ago, my firefox browser started not restoring the previous sessions. I changed nothing in the configuration and I don't remember I had a crash. The option "Restore Previous Session" does not appear in the "3-bar menu > history" and it appears grayed in the History Firefox main menu. What I've already tried or verified following the instructions of mozilla forum: 1) Settings > general > “Open previous windows and tabs” is checked as it always have been; I unchecked and and rechecked but nothing changed; 2) Settings > Privacy & Security > “remember history” is selected. Also tried to Settings > Privacy & Security > "Use custom settings for history" with "Always use Private Browsing mode" not checked. No success 3) I also deleted sessionstore-backups folder under my profile. The new created folder, even after closing some new sessions, has only the "recovery.jsonlz4" and "recovery.baklz4" files. There is no "previous.jsonlz4" inside which seems weird. 4) through about:config I checked that browser.sessionstore.resume_from_crash was true. In fact, I have Firefox in a second computer with no sessions restoring problem. I compared all browser.sessionstore.xxxx variables and the values are the same. I still have the problem and do not know what to try next. Reset Firefox?