The first step is properly closing Firefox before you shutdown the computer. *https://support.mozilla.org/en-US/kb/restore-previous-session Use one of these to close Firefox if you are currently doing that by clicking the close X on the Firefox Title bar, especially if you have multiple windows or Private Browsing windows open to prevent losing tabs in unnoticed windows. *"3-bar" menu button -> Exit (Power button) *Windows: File -> Exit *Mac: Firefox -> Quit Firefox *Linux: File -> Quit