Sorry to hear about the inconvenience. You can rescue saved session data from your profile folder, but I'm not sure of the most convenient way to restore it. '''''Firefox's Session Restore Feature''''' To restore your immediately previous session, check for "Restore Previous Session" in one of these locations: * Application menu ("3-bar" button at the right end of the toolbar) * top menu bar > History If Restore Previous Session is available, you can click that. If it's grayed out, either Firefox already restored the session or it was not able to restore it. When a session has been restored, you can use Recently Closed Windows and Recently Closed Tabs to recover missing windows/tabs from that session, either from the History menu on the top menu bar or the "Library" toolbar button > History sub-menu. '''''Locating Session History Files''''' By default, Session Manager creates a folder named '''sessions''' in your currently active Firefox profile folder. Here's how to look for that. 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, find the Profile Folder row and click the "Show in Finder" button (for Windows, "Open Folder" button). This should launch a new window listing various files and folders in Finder / Windows Explorer. The '''sessions''' folder contains files stored by Session Manager. Optionally, these files can be encrypted, but assuming they are not, they probably could be restored the same way you would restore a Firefox session history file. The '''sessionstore-backups''' folder contains files stored by Firefox's built-in session history feature. Firefox's feature saves the immediately previous session, and snapshots of your tabs from the time of the most recent Firefox updates. '''''Inspecting a Session History File''''' Newer compressed files (.jsonlz4 extension) and older uncompressed files (.js extension) can be viewed using a tool on my website. Drag and drop a file from Finder / Windows Explorer onto this page: https://www.jeffersonscher.com/res/scrounger.html Then click Scrounge URLs to show the file's contents. Can you find the one you want to use? ''Edit: I added a button to save a Session Manager .session file to a sessionstore.js file that you can use to restore the session to Firefox.'' '''''Replacing the latest Session History file with an older one''''' This is the classic technique to trick Firefox into restoring a different previous session. Since it involves many steps and this post already is quite long, I'll come back to this if you have a file you want to restore.