30 seconds: The button you're probably missing
Had a client last month—small law firm, four partners, each had forty-plus tabs open for case research. Firefox updated overnight, and bam—next morning, single blank tab staring at them. Panic city.
Look in the top-right corner of Firefox. See that little icon that looks like a page with a curved arrow? That's the "Restore Previous Session" button. Click it. Nine times out of ten, your tabs come back. If you don't see it, click the hamburger menu (three horizontal lines top right) and look for "Restore Previous Session" in the History section.
If that worked, you're done. Go back to work. If not, move on.
5 minutes: Dig into the History menu
The button's not there? We'll find it manually.
Step 1: Open the History menu
- On Windows/Linux: press
Ctrl+H - On Mac: press
Cmd+H
Or click the hamburger menu → History.
Step 2: Look for "Recently Closed Windows"
If Firefox crashed, your old window (with all its tabs) is usually listed here. Click it. If you see multiple windows from before the crash, pick the one with the most tabs. I've seen people miss this because they only check "Recently Closed Tabs"—that's a different list.
Step 3: Check the Library window
Still nothing? At the bottom of the History menu, click "Show All History." In the Library window that opens, look on the left sidebar under "History" for entries marked with today's date and a time just before the crash. Double-click any entry to restore that window's tabs.
Used to work for me on Firefox 115 and still works on 125+. If this got your tabs back, great. If not, we go deeper.
15+ minutes: Resurrect tabs from Firefox's backup files
Firefox keeps automatic backups of your session—about 10 to 20 rolling copies. The UI sometimes forgets to show them, but the files are still there. Here's how to pull them out.
Step 1: Open your profile folder
Type about:support in the address bar and hit Enter. Look for the row called "Profile Folder"—click the "Open Folder" button next to it (on Windows) or "Show in Finder" (on Mac). That's where Firefox stores everything.
Step 2: Close Firefox completely
Do not skip this. If Firefox is running, it will overwrite these files when you try to restore. File menu → Exit, or right-click the Firefox icon in your taskbar and close it.
Step 3: Find the session backup files
In your profile folder, look for these files:
sessionstore.jsonlz4
sessionstore-backups/
├── recovery.jsonlz4
├── recovery.baklz4
├── previous.jsonlz4
└── upgrade.jsonlz4-20241108233408The sessionstore-backups folder is your goldmine. The previous.jsonlz4 file is from the last time Firefox started successfully. The upgrade*.jsonlz4 files are dated backups from each update. Pick the one with the most recent timestamp before your crash.
Step 4: Restore from a backup
Copy the backup file you want (say, previous.jsonlz4) to a safe location—maybe your desktop. Then delete or rename the original sessionstore.jsonlz4 file in your profile folder. Now rename the backup to sessionstore.jsonlz4 and move it into the profile folder. Start Firefox. Your tabs should load.
If you get an error or blank tabs, try another backup file. I've had clients where recovery.baklz4 had the goods when previous.jsonlz4 didn't.
Step 5: Use the Scrounger tool (optional, advanced)
If manual restore fails, install the Session Berry add-on. It can read those backup files directly and let you pick individual windows to restore. Saved my bacon on a Windows Server 2019 machine that had Firefox crash during a Remote Desktop session—200 tabs gone. Session Berry pulled 198 of them back.
Preventing this from happening again
Once you've recovered, do these two things:
- Turn on Firefox's own backup: In
about:preferences#general, check "Open previous windows and tabs" under Startup. That tells Firefox to save session data every 10 seconds instead of every 30. - Install an add-on: Session Berry or Tab Session Manager gives you manual save-and-restore control. I use Tab Session Manager on my own machine—backup to a local JSON file every 5 minutes. When Firefox goes sideways, I just import that file.
Real talk: This bug happens most often when Firefox updates in the background while you're using it. The session file gets partially written during the update, then the old file gets replaced. Mozilla's aware of it—they fixed a related bug in Firefox 113 but it still bites people. If you're on an older version like 102 ESR, you're especially vulnerable.
Bottom line: don't panic. Your tabs aren't gone—Firefox just lost the map. You've got the map now. Get back to work.