I realize this comes very late (unless you've been asleep the past 7 hours), but:

Don't exit Firefox! Or if you already did, don't start it back up again!

If Firefox is running: Open your current Firefox settings (AKA Firefox profile) folder using either

• "3-bar" menu button > "?" button > Troubleshooting Information
• (menu bar) Help > 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. This should launch a new window listed various files and folders. For best results, change the view to "Details".

(If Firefox not running, get to this folder by pasting the following in the Run box on the start menu and pressing Enter: %APPDATA%\Mozilla\Firefox\Profiles and then double-click into the most recently updated semi-randomly-named folder you find there.)

In the window that launches, scroll down and double-click into the sessionstore-backups folder. Save all files here to a safe location, such as your Documents folder, so Firefox doesn't overwrite them. We may be able to use them to recover your lost tabs.

Also, if you return to the main level of the profile folder, you may find some sessionstore files. Copy those to the safe location as well.

Could you report back on what you found?

Note: If Windows hides the .js file extension from you, you can change a setting so that you can see all file extensions (this helps when renaming files). This support article has the steps: http://support.microsoft.com/kb/865219 or http://windows.microsoft.com/en-us/windows/show-hide-file-name-extensions

The kinds of files you may find among your sessionstore-backup files are:

• recovery.js: the windows and tabs in your currently live Firefox session (or, if Firefox is closed, your last session)
• recovery.bak: a backup copy of recovery.js
• previous.js: the windows and tabs in your last Firefox session
• upgrade.js-build_id: the windows and tabs in the Firefox session that was live at the time of your last update

Regarding history, can you see any pattern as to what is saved and what isn't? Firefox doesn't save history for pages you visit in a private window, but otherwise, I can't think of any distinction between sites.

jscher2000 said

I realize this comes very late (unless you've been asleep the past 7 hours), but: --- The kinds of files you may find among your sessionstore-backup files are:

• recovery.js: the windows and tabs in your currently live Firefox session (or, if Firefox is closed, your last session)
• recovery.bak: a backup copy of recovery.js
• previous.js: the windows and tabs in your last Firefox session
• upgrade.js-build_id: the windows and tabs in the Firefox session that was live at the time of your last update

Thanks a lot! Unfortunately my firefox crashed several times last night due to a full ram memory and the backup session history is gone forever. The backup histories in the main folder are ancient and likewise of no help.

However, thankfully an upgrade.js fie seems to exist from yesterday at around the time of the accident. I think it might have the backup, it's actually possible that it was the update that cleared the session restore rather than me closing the firefox (I did not close it in the usual way). On the other hand I don't remember any updates taking place and the file is somewhat smaller than usually and the session was large... Crossing fingers here.

Anyway, how do I go about restoring the backup? Do I just rename the "upgrade.js" to "recovery.js" and overwrite?

Note that Firefox 36.0.4 has been released that has fixes of more recently disclosed security vulnerabilities.

• https://www.mozilla.org/en-US/firefox/36.0.4/releasenotes/

You can create a backup of all files in the sessionstore-backups folder and copy this upgrade file to sessionstore.js in the main profile folder.

If you do not use "Show my windows and tabs from last time" then you need to check for "History > Restore Previous Session" and possibly History > Recently Closed Tabs/Windows

Hi Angry_Firefox, as noted by cor-el, the file that Firefox will restore is called sessionstore.js and it is in the main level of the profile folder, not in the sessionstore-backsups folder.

This file is created when Firefox shuts down, and removed after it starts up again, so in order to make the switch, you need to exit Firefox, rename the current sessionstore.js, then copy in the file you want to try and rename it to sessionstore.js, then start Firefox. If Firefox is not set to restore your previous session automatically, check the History menu for Restore Previous Session.