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
• maybe some .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.

Hello, thank you very much for the post. yeah theres no option in any menu in the browser for restoring previous session

in my sessionstore-backups folder id like to restore my previous.jsonlz4 contents as it was last updated yesterday which would be a very suitable restoration point

since i have so many tabs the scrounger website keeps crashing in both firefox and chrome when i try to post my file there. with firefox i can scroll up and down with my mousewheel and it will show it but if i grab the scroll bar on the side and scroll even a bit down the whole tab crashes. with chrome the file doesnt even load

is there a way to load this file so that firefox restores all of my tabs?

Okay, here's what you can try:

Overview

(1) Normal Firefox shutdown (2) Hide the old session history files in sessionstore-backups (3) Replace the sessionstore.jsonlz4 file with a copy of previous.jsonlz4 (and rename it to sessionstore.jsonlz4) (4) Start Firefox and hope it uses the replacement file

In More Detail

(1) From inside Firefox, 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" button. This should launch a File Explorer window listing the various files and folders in your profile.

Leaving that window open, switch back to Firefox and Exit, either:

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

Pause for several seconds to let Firefox finish its file maintenance and fully shut down.

(2) Right-click the sessionstore-backups folder, click Rename, and change it to sessionstore-backupsOLD

(3) Right-click the sessionstore.jsonlz4 file, click Rename, and change it to sessionstoreOLD.jsonlz4

Copy/paste the previous.jsonlz4 file into this folder. Right-click it, click Rename, and change it to sessionstore.jsonlz4

(4) Start Firefox and it should read the swapped in sessionstore file and restore whatever was in the substitute file; if you do not have Firefox set to restore your previous windows and tabs automatically, use History > Restore Previous Session

Any luck?

How big is this file?

The normal procedure to use a backup is to place the file in the profile folder with Firefox closed and rename the file to sessionstore.jsonlz4.

See also:

• /questions/1205358#answer-1078508 Can't decompress recovered jsonlz4 session file

thank you so much for the help. the tabs are back, ive enabled my addons and my theme, closed and reopened my browser again and it all seems great now. this does wonders for my mental health so this is quite a big impact for me and ill get to work on cleaning up my 2000+ tabs right away, no more taking it for granted. (they're mainly youtube/reddit posts). i assume i dont have to unhide or do anything extra for now

@cor-el the previous.jsonlz4 file was 39MB's. somehow every other more recent file was 40-44MB's despite only being a few tabs in a few windows. otherwise as to how the scrounger manages to crash assuming its not supposed to, yeah im guessing its the 2000 tabs