Sorry for the delay, your question ended up under iOS (iPhone, iPad) instead of desktop (Mac).

Can you try one of these:

• (menu bar) History menu > Recently Closed Windows
• menu button > Library > History > Recently Closed Windows

Firefox normally remembers up to three closed windows.

Yeah, I tried the "reopen closed windows" & it didn't work.

cje24576 said

Yeah, I tried the "reopen closed windows" & it didn't work.

The window was already gone from the list?

Let's see whether there are any older session history files that might help.

Could you start by making a backup of your existing session history files? Here's how:

(1) To open your profile folder...

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 "Show in Finder" button. If Finder is showing a bizarrely named folder, double-click that so you can see the files and folders inside.

(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 or Desktop.

(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
• old stuff that won't help

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 window?

To preview the contents of a file, you can drag and drop it onto the white box on 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.

I don't see any of those files. I see a "sessionstore.js" file from 2017. But that's really old. Now, I have been using the internet since I noticed the issue (trying to find solutions) & looking through my browser history to see if I can find all my tabs.

Your website worked though! Thanks so much! definitely going to bookmark your site for the future.

I hope that means you were able to find a more recent file and didn't have to start from 2017!