This is not so much a question, as an answer that some people desperately need. Ever since Version 34, Firefox has done a superb job of restoring the tabs that the user has created, either on restarting Firefox (if that option is chosen) or on request. The details of how to restore tabs are covered in Firefox's basic help online, and even how to deal with several crashes in a row (such as in an addon) ruin the normal backup file are also well explained. However, today I accidentally pressed Alt+F4 twice on my poorly-designed keyboard and closed my main window, with 93 tabs, and another Firefox window as well. I'm not sure this is exactly what happened, but I lost all 93 of my tabs. I read many of the postings in which people give various suggestions, but none worked. Every time I restored a version of the sessionstore.js file I saw the same lonely empty tab. Restoring prefs.js did nothing, and neither did making changes in the internal configuration constants. I tried refreshing/resetting Firefox (which preserves bookmarks), but I still couldn't restore the tabs. It was now clear that the problem was in sessionstore.js (and all its backups) for sure. I'm writing this for people who must restore their windows or tabs, and don't mind getting technical about it. That was my situation. The solution was to realize that the sessionstore.js file contains JSON code, which is an efficient way to represent integers and strings arranged in a tree structure. I figured there must be a JSON editor somewhere, and it turns out there is a great one available online, at www.jsoneditoronline.org . It can read a file on your computer, edit it, then save it back on your computer. As soon as I viewed sessionstore.js in the editor, it was obvious how easy this was going to be. The top level of the tree is understandable. I simply grabbed the data representing the window with 93 tabs, and dragged it from the list of closed Firefox windows to the list of open windows. This automatically moved the history of each tab, and even the strings entered into forms. After copying sessionstore.js back to the Firefox profile, I started Firefox one more time. The playing of Pandora signalled that my tabs were back and functioning once again. Now, editing JSON code is not something that everyone is ready for. And your problem might not be reflected in the JSON tree so simply. But, for technical-minded people who don't want to lose their tabs or windows to a mistake or a crash, this technique can be just what's needed when everything else fails.