So one possible variable is your startup setting. You can double-check here to make sure you don't have Firefox set to restore your windows and tabs from last time: [[Startup, home page and download settings]]. A second possibility is that you have a user.js file in your settings folder (Firefox profile folder) that specifies that even though you normally don't restore your previous session, Firefox should do it just this one time. Of course, since Firefox rereads user.js every time you start up, it becomes permanent. This article describes how to track down and remove a user.js file: [[How to fix preferences that won't save]]. A third possibility is that Firefox is crashing during shutdown, and Firefox is doing a standard post-crash recovery. If the other two theories are not applicable, I suggest switching what Firefox does post-crash to see whether this is the problem. To change Firefox from restoring automatically after a crash to presenting a list of previous session windows and tabs: (A) In a new tab, type or paste '''about:config''' in the address bar and press Enter. Click the button promising to be careful. (B) In the search box above the list, type or paste '''sess''' and pause while the list is filtered (C) Double-click the '''browser.sessionstore.max_resumed_crashes''' preference and enter 0 (that's a zero) and click OK. The next time Firefox starts if you get the screen saying "this is embarrassing" and showing a list of your last session tabs, then the problem is that Firefox is crashing during shutdown.