Sorry to hear about this problem and for the delay in getting back to you. Firefox stores your open

Sorry to hear about this problem and for the delay in getting back to you.

Firefox stores your open windows and tabs in a file named sessionstore.js in your currently active settings folder. Could you check that folder and back up all of the sessionstore files as the first step.

Open your current Firefox settings (AKA Firefox profile) folder using

Help > Troubleshooting Information > "Show Folder" button

If you find a file named sessionstore but not sessionstore.js, Windows may be hiding file extensions from you. To work with files as accurately as possible, I suggest unhiding them. This Microsoft support article has the steps: http://support.microsoft.com/kb/865219.

(In Windows 8.1, you should be able to access the Folder Options dialog by tapping the Alt key to show the menu bar, then using the Tools menu. Click to the View menu and scan down for the hidden files/folders option.)

Assuming you still have a sessionstore.js or sessionstore.bak file that would have your pre-update session, check out these threads for different ways to rescue the lost URLs from the sessionstore.js or sessionstore.bak 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/