Unfortunately, your Firefox settings were stored under your user folder:

C:\Users\username\

and not in the Program Files.

When you resintalled, did Windows create a folder named:

C:\Windows.old\Users\username\

If Yes, we can assist in digging through that.

If No, you may need to use a deleted file recovery tool like the following to try to find the old settings files:

https://www.piriform.com/recuva

I can mention some files to look for if you have to do that.

Also, what files do you have inside the sessionstore-backups folder? Please make sure you have a safe copy far away from Firefox's folders. If the contents seem to be the right date/time and file size to have your missing tabs, you can try loading them as follows:

(1) Open your profile folder as follows

If Firefox is running: You can 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 shoud launch a new window listing various files and folders.

If Firefox is not running: Type or paste the following into the Start menu search box and press Enter:

%APPDATA%\Mozilla\Firefox\Profiles

If you see one semi-randomly-named folder, click into that. If there are multiple folders, find the most recently updated one and click into that.

(2) If Firefox is still running: Leaving that window open, switch back to Firefox and Exit, either:

• "3-bar" menu button > "power" button
• (menu bar) File > Exit

Pause while Firefox finishes its cleanup... this may take a minute.

(3) Rename sessionstore.js to something like sessionstore.old

Note: By default, Windows does not show the .js file extension. If you see a file (not folder) named sessionstore which has the type JScript, that most likely is sessionstore.js. I recommend switching Windows to showing file extensions using the steps in this Microsoft support article: http://windows.microsoft.com/en-us/windows/show-hide-file-name-extensions just to be sure.

(4) Copy the file you want to try (old recovery.js or other) into this profile folder and rename it to sessionstore.js

(5) Start Firefox. If your session is not resumed automatically, use History > Restore previous session. Firefox should display the tabs from the file you copied into the profile folder.