Make sure that you not run Firefox in Private Browsing - Use Firefox without saving history mode. In Private Browsing mode some menu items are disabled (grayed) and some features like visited links and others are disabled and not working. You are in Private Browsing mode if you see "Tools > Stop Private Browsing". See Private Browsing - Use Firefox without saving history and http://kb.mozillazine.org/Issues_related_to_Private_Browsing ..... You enter Private Browsing mode if you select: Tools > Options > Privacy > History: Firefox will: "Never Remember History" To see all History settings, choose: Tools > Options > Privacy, choose the setting Firefox will: Use custom settings for history UnCheck: [[ ] "Automatically start Firefox in a private browsing session"

Menu differences: Windows: Tools > Options - Mac: Firefox > Preferences - Linux: Edit > Preferences

My 'Recently Closed Tabs' and 'Recently Closed Windows' are grayed out as well. My problem is that i used to have multiple windows open and now they are all gone. I really need to get them back. They are not in my history. I am running Mac OS X Version 10.5.8.

Hi, registered to share my solution as I had this problem too. I made sure that my history *was* recorded and that privacy mode wasn't turned on. it seemed that the values browser.sessionstore.enabled and browser.sessionrestore.max_tabs_undo in about:config was edited so no tabs could be restored. I simply reset them to the default values and no ctrl+shift+t works again.