As the first step, could you back up all the sessionstore files in your currently active Firefox profile folder? Here's how:

If Firefox is already running:

Open your current Firefox settings (AKA Firefox profile) folder using any of these:

• "3-bar" menu button > "?" button > Troubleshooting Information
• Help menu > Troubleshooting Information
• type or paste about:support in the address bar and press Enter

In the first table on the page, click the "Show Folder" button

Scroll down and copy all files that start with sessionstore to a safe location, such as your Documents folder, in case you need to use them for recovery. Otherwise, there's a good chance Firefox will overwrite them.

If Firefox is not running:

Don't start Firefox. Type or paste the following in the search box on the Start Menu:

%APPDATA%\Mozilla\Firefox\Profiles

Usually you will find one folder with a partially random name. If you find more than one folder, click into the most recently updated one.

Scroll down and copy all files that start with sessionstore to a safe location, such as your Documents folder, in case you need to use them for recovery. Otherwise, there's a good chance Firefox will overwrite them.

Next... back in Firefox, I assume you already restored your previous session (e.g., History menu > Restore Previous Session)? If you do not have any closed windows available for re-opening, we may need to salvage URLs from the older sessionstore files. However, before listing a lot of steps, can you update us on what you found?

Sorry for the delay but I do not know how to copy the data from the "Show Folder". The latest session are in the last day. How can I send this info? In addition, there are 27 numbered sessionstores beginning in 2009 and ending in 2012.

The numbered sessionstore files can indicate that the regular file was locked or corrupted, so Firefox had to keep creating new ones. It sounds as though those are all old so probably not relevant to your current needs.

To copy files from one folder to another, you can select them (Ctrl+click to select multiple files), then right-click any one of the selected files and choose Copy. Then open your Documents folder, right-click a blank area, and Paste.

This is for safekeeping and doesn't send information to the forum or to me.

When you check the dates/times on the files, are any of them from the time of your last shutdown when you had the window open?

There was a sessionstore.bak 15 KB at 4:05 P.M. which is a few hours after I ran a cleaner from Simplitec >> Bad idea!

Thank you for helping Mr. Scher. I have reopened Firefox and the History Window remains grey. Also, I forgot to mention that the Simplitec program apparently deleted my Windows 7 Restore Points.

To see what is in that sessionstore.bak, you could try one (or more) of the data mining techniques in these posts to rescue the URLs from the file:

• Using Firefox's Browser Console (formerly known as Error Console): https://support.mozilla.org/questions/969046#answer-471950

• Using Firefox developer tool "Scratchpad": http://forums.mozillazine.org/viewtopic.php?f=38&t=622036&start=60&p=12098147#p12098147

• Using a third party website: https://firefox-session-restore.herokuapp.com/

If you need to go back further in time, one possibility is Windows' "Previous Versions" tab.

You should not restore an old file while Firefox is running, but you can take a look at the tab and see whether there are any old versions that might be useful.

Right-click the sessionstore.js file in your Firefox profile folder (not the backup) and choose Properties, then the Previous Versions tab. Can you find any copies from the relevant time frame?

Edit: If you do not have any restore points, then you likely will not find any Previous Versions.

Looks like I am "dead in the water". Is there a way to have the History restore "Recently Closed Windows" so it won't be greyed out in the future?

Unless your settings changed, Firefox should be creating/storing new session history as you browse. You can peer into your profile folder and check the timestamp on sessionstore.js (it is updated every 15 seconds when you are active). I guess the question is, can you trust that it will be there when you exit and restart the browser?

Could you check for customized session history settings in Firefox's about:config preferences editor. Here's how:

(1) In a new tab, type or paste about:config in the address bar and press Enter. Click the button promising to be careful.

(2) In the search box above the list, type or paste sess and pause while the list is filtered

(3) Review the preferences starting with:

• browser.sessionhistory.
• browser.sessionstore.

If you see bolded entries, which indicates that they vary from the default setting, could you right-click > Copy and post in a reply to see whether they might be relevant to this problem? (Other than the one you changed intentionally.)

You also could consider some extra backups. The Session Manager extension has options to (1) create a backup when you exit Firefox, and (2) locate it in a different folder where, presumably, cleaning tools are less likely to look for them. I haven't tested this, but might be useful as extra insurance.

• https://addons.mozilla.org/firefox/addon/session-manager/
• http://sessionmanager.mozdev.org/options.html#advanced ("allows the user to override the default location for storing saved sessions")

Also, if a set of tabs is really critical, consider using the Bookmark All Tabs feature to store them in your bookmarks. I believe this only gets the visible tabs, so if you have multiple tab groups in the same window, you might need to save each one separately. Right-click any tab in the window to use Bookmark All Tabs.

Speaking of tab groups, just in case your tabs are present in a different group, could you open the tab group page using Ctrl+Shift+e to check? You can press the Esc key to return to where you were, or click a new destination.

Hi, browser.sessionstore.upgradeBackup.latestBuildID;20140506152807 is in bold. Should I change my bolded windows to default or can it be left at 10? There is only the existing tab group. Again, thanks for your help.

I think your preferences are fine. So probably that cleanup utility is to blame and things should be working going forward. Hopefully!

I wish we had this "discussion" long ago. Your instruction on how to simply Bookmark All Tabs with a single click should be on the front page of a Firefox "How To"! Still I would feel better if my History Recently Closed window was not greyed out.

The Recently Closed Windows list (or on the new menu, Restore Closed Windows list) should only be grayed out/empty if there is nothing to restore.

If you open a few windows (e.g., right-click a bookmark > Open in New Window a few times) then close them, does the menu work as expected?

If it doesn't work, and you are not starting in a private browsing window, then something definitely is broken...