If the Restore Previous Session is greyed out, there might be something wrong with the files that store your recovery sessions. If you've previously made a copy of the files, you can use them to restore your sessions.
Here's how:
- Open the profile folder.
- Close Firefox
- In your profile folder, give the following recovery files another name:
- previous.js
- recovery.bak
- recovery.js.
- Put your backup recovery files into the Profile folder.
- Open Firefox.
To prevent this from happening again, change your Tab preferences and settings or use the Session Manager add-on to regularly back up your profile.
