Two initial notes: First, you always have the option to do a proper Firefox shutdown before putting your computer to sleep. Please allow 30 seconds for file maintenance Firefox does during shutdown. Second, you may want to consider using Hibernate instead of Sleep. This writes the contents of memory to disk and requires almost no power to maintain. https://support.microsoft.com/en-us/help/13770/windows-shut-down-sleep-hibernate-your-pc '''Why would Firefox restore an older session?''' When Firefox detects a crash condition, it works through the available session history files from most recent to oldest. Perhaps the crash is corrupting the most recent files somehow? Firefox also has the option to create multiple profiles -- each with its own separate history. I will add a section at the end of this reply about checking for that in case Firefox is starting up in different profiles at different times. ''Session Manager Add-on Option'' There also are session management extensions you could consider which might provide a backup when the built-in feature fails. These are the ones I'm aware of that you might investigate/try out: ''Use database storage -- also may be damaged by power-off crashes:'' * https://addons.mozilla.org/firefox/addon/tab-session-manager/ * https://addons.mozilla.org/firefox/addon/session-boss/ ''Use bookmark storage -- also may be damaged by power-off crashes:'' * https://addons.mozilla.org/firefox/addon/session-sync/ * https://addons.mozilla.org/firefox/addon/my-sessions/ Bookmark storage is more robust in that Firefox backs it up regularly. However, having the extra data show up when you are searching your bookmarks may be annoying. - - - - '''''Multiple Profile Folder Exploration''''' '''Profile Manager Page''' Inside Firefox, type or paste '''about:profiles''' in the address bar and press Enter/Return to load it. This page should list at least one profile and could list many. (Each profile has two folders and one or more buttons. Do not use any Remove buttons!) The profile that Firefox is currently using will have this: '''This is the profile in use and it cannot be deleted.''' Do you have another profile named '''default''' or '''default-release''' or default-''longnumber'' listed on this page? If so, you can check whether it is the one you were using recently by clicking its '''Launch profile in new browser''' button. If it isn't what you want, simply close that new window. If it IS what you want, back on the about:profiles page, click the '''Set as default profile''' button for that profile so Firefox uses it automatically at the next startup. Any interesting profiles besides your main one?

You can also check if you have a sessionstore.js file in the profile folder that Firefox might be using as fallback if sessionstore.jsonlz4 is missing for some reason.