Do you have Firefox set to restore your previous session automatically? If not, have you already used the menu option:

• "3-bar" menu button > Restore Previous Session
• (menu bar) History > Restore Previous Session

If those are missing or grayed, check either:

• "3-bar" menu button > Library > History > Recently Closed Windows (and within each restored window, Recently Closed Tabs)
• "Library" toolbar button > History > Recently Closed Windows (and within each restored window, Recently Closed Tabs)
• (menu bar) History > Recently Closed Windows (and within each restored window, Recently Closed Tabs)

If your missing windows are not listed there:

Firefox creates numerous session history files, but because session history is only for the immediately previous session, it is unfortunately too easy to lose it. Could you start by making a backup of your existing session history files? Here's how:

Do not exit Firefox, or if you closed it, don't re-open it.

(1) To open your profile folder...

If Firefox is still running:

You can open your current Firefox settings (AKA Firefox profile) folder using either

• "3-bar" menu button > "?" Help > 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 "Open Folder" (or "Show in Finder") button.

If Firefox is closed:

Type or paste the following into the Windows Run dialog or the system search box and press Enter to launch Windows Explorer:

%APPDATA%\Mozilla\Firefox\Profiles

In that folder, do you see a semi-randomly-named folder? If so, click into it. If you find multiple such folders, find the one that was most recently updated.

(2) Copy out session history files

In your profile folder, double-click into the sessionstore-backups folder. Save all files here to a safe location such as your Documents folder.

(3) What files did you find?

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

• recovery.jsonlz4: the windows and tabs in your currently live Firefox session (or, if Firefox crashed at the last shutdown and is still closed, your last session)
• recovery.baklz4: a backup copy of recovery.jsonlz4
• previous.jsonlz4: the windows and tabs in your last Firefox session
• upgrade.jsonlz4-build_id: the windows and tabs in the Firefox session that was live at the time of your last update
• .js files from Firefox 55 or earlier

Could you take a look at what you have and the date/time of the various files to see whether you think any of them would have the missing tabs?

To preview the contents of a file, you can drag and drop it onto this page, then click Scrounge URLs: https://www.jeffersonscher.com/ffu/scrounger.html

That tool is on my site, so please let me know if it doesn't work for you.

You can try to reboot another time in case something went wrong on the Windows OS level to see if that has effect.

Restarting my pc etc doesnt change anything. I also looked up a few things on this forum but nothing helped.

You can look at this utility to browse System Restore points to see whether there is previous version of the sessionstore files (sessionstore.jsonlz4 or files in the sessionstore-backups folder) with that lost session.

• System Restore Explorer
  https://www.nicbedford.co.uk/software/systemrestoreexplorer/

You can inspect the files with the above posted scrounger tool.

I'm not sure if i'm doing anything wrong but for now it doesnt find anything.

Hi JustLeon, let me give you a more step-by-step description for that tool in case their documentation was incomplete:

Finding/Using Shadow Copies

You can use a utility program to search inside restore points to try to locate an old file that's usable. (Please do NOT try to use the built-in Windows System Restore for this because you would lose too much data.) Here are the steps:

(1) Set Windows to show hidden files and folders:

https://support.microsoft.com/en-us/help/14201/windows-show-hidden-files

(2) Download and run one of these two programs:

• System Restore Explorer: http://nicbedford.co.uk/software/systemrestoreexplorer/
• ShadowExplorer: http://www.shadowexplorer.com/

Within the most recent restore point shown in the program, you can explore along this path to see whether you can find a shadow copy of your profile:

\Users\your-user-name\AppData\Roaming\Mozilla\Firefox\Profiles\

(3) Check in the sessionstore-backups folder for older backups. You can export interesting files to a convenient location such as your currently live desktop. Then you can use the Scrounger tool to view their contents.