If "History > Restore Previous Session" is disabled (grayed) then you can't restore the previous session and you can consider this session as lost. If you still have the history then you can try to restore those tabs.

Use "Firefox > Exit" (Windows: Firefox/File > Exit; Mac: Firefox > Quit Firefox; Linux: Firefox/File > Quit) to close Firefox if you are currently doing that by clicking the close X on the Firefox title bar.

You can reset browser.sessionstore.* prefs that are user set (bold) to the default value via the right-click context menu on the about:config page to make sure that Session Restore is enabled and working properly.

• http://kb.mozillazine.org/Session_Restore
• https://support.mozilla.org/kb/restore-previous-session

Since two or three days I have noticed that mozilla has opened all my tabs from the last session by itself, not started from a restore button. And there is no more a button to start the last session again ! From that point of change I have lost my several windows and tabs, so that I was used to build up all my tabs again. And if it is to do with a new version of mozilla firefox, I would think about it much better, to let it to be chosen from me as user, if I would taste to start my last session in mozilla firefox through myself with a start-button or through mozilla firefox to open all tabs alone by itself !

best regards pemigabo123

In Options\General\Homepage you can choose "reopen all last tabs" at opening your browser.

You can check if you have an user.js file in the Firefox profile folder that sets the browser.sessionstore.resume_session_once pref to true.

• http://kb.mozillazine.org/browser.sessionstore.resume_session_once

• http://kb.mozillazine.org/about:config