If these --

• "3-bar" menu button > History > Restore Previous Session
• (menu bar) History > Restore Previous Session

-- are missing or grayed out, check either:

• "3-bar" menu button > History > Recently Closed Windows
• "Library" toolbar button > History > Recently Closed Windows
• (menu bar) History > Recently Closed Windows

Can you find any recently closed windows to restore?

What was this part -- what did you try to tweak:

I've gone into the file and tried to tweak it.

Firefox creates an extra session history file when it updates, so you could look for that and see what tabs are in it. 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 > More Troubleshooting Information
• (menu bar) Help > More 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 "Open Folder" button. This should launch Windows' File Explorer listing the contents of your current profile folder.

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

Sometimes you can tell from the last modification time which one will have your missing tabs, but not always.

Optional File Contents Preview

These compressed files are a pain to view, so I created a tool on my website to list out their contents. If you want to try that, you can drag and drop it onto the large box on the following page, then click the "Scrounge URLs" button:

https://www.jeffersonscher.com/ffu/scrounger.html

If you don't get a list within 15 seconds, that probably means the script is caught in a loop. You may need to close the tab to avoid a tab crash and then try again in a new tab.

If you get a useful list, use the "Save List" button to archive it as a web page of clickable links for future reference, in case no other approach is successful.

I'm not sure Sync will be useful for recovering old tabs. Firefox usually synchronizes those in real time, and I'm not sure you can get previous session tabs back using Sync, the list always seems to be current. ??

.....this is utterly RIDICULOUS - should be far, FAR easier to recover any previous session open within a REASONABLE amount of time before (like, 20 minutes????} and it's just a demonstration of Mozilla's comparatively-newfound, DISGUSTING contempt for its users; interface / platform provided ['scrounger'] keeps disappearing - refuses to refresh - so, just duplicated it AGAIN and, UNlike previously appears NO way of SIMULTANEOUSLY reopening 205 tabs (I really do HOPE you're NOT judging me for THAT.....)

Get your effin' ACT together, already - absolutely AMATEUR hour conditions at present.....

Hi ogam5, unfortunately Firefox has never had a built-in feature to restore anything other than the immediately previous session. There have always been add-ons to store additional sessions.

For your immediate needs, have you identified the file you want to restore? The purpose of my Scrounger page is to preview a file's contents. If that isn't working, maybe you can judge by the time stamp on the file which one is most likely to be the set of tabs you want to roll back to.

Once you know the file you want to use, this is the process for tricking Firefox into thinking it's the latest session history file:

(1) Open your current Firefox profile folder in Windows File Explorer as described earlier

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

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

Pause while Firefox finishes its cleanup -- a file named sessionstore.jsonlz4 should appear in the folder.

(3) Once Firefox has stopped updating things:

right-click > Rename sessionstore.jsonlz4 to sessionstoreOLD.jsonlz4

That preserves your latest session just in case you need it later.

(4) Copy/paste the file you want to restore into this folder and rename it to the name Firefox will be looking for. For example:

• recovery.jsonlz4 => sessionstore.jsonlz4
• previous.jsonlz4 => sessionstore.jsonlz4
• upgrade.jsonlz4-20230214051806 => sessionstore.jsonlz4

(In other words, whichever old file you are rolling back to, it needs to be renamed to sessionstore.jsonlz4)

(5) 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?