What do you have set here? see screenshot

That screen looks different from mine.

Wrong option for history. see screenshot Click settings to see the 2nd screenshot

You want to use Custom setting for history and then click on settings.

Ah! Okay. It is not checked.

See screenshot.

Then it should look like this. see screenshot

Okay, I did that.

Open a bunch of tabs, close the browser and reopen it and see what happens.

Firefox opened the tabs when I restarted it.

Mark it as resolved and get back to life.  ;-))

But, my question was: how can I recover the tabs that were open before? Is there any way to retrieve them from history?

If the history is there, you use the "Recently Closed Tabs" option. see screenshot

When this problem first occurred, the Recently Closed Tabs option showed no tabs - even though there had been tabs open.

I just cleared my history and if your menu looked like this then the history was gone. see screenshot

I still have the older history. I just need the tabs that were open that should have reopened. How does Firefox know to reopen tabs? Is there a temporary cache I might access?

This may help you.

https://support.mozilla.org/en-US/questions/1220435

You will normally find these files in the sessionstore-backups folder:

• previous.jsonlz4 (cleanBackup: copy of sessionstore.jsonlz4 from previous session that was loaded successfully)
• recovery.jsonlz4 (latest version of sessionstore.jsonlz4 written during runtime)
• recovery.baklz4 (previous version of sessionstore.jsonlz4 written during runtime)
• upgrade.jsonlz4-<build_id> (backup created during an upgrade of Firefox)

You can copy a file from the sessionstore-backups folder to the main profile and rename the file to sessionstore.jsonlz4 to replace the current file with Firefox closed.

• make sure to backup the current sessionstore.jsonlz4

You can look at this tool to inspect a compressed sessionstore file.

• https://www.jeffersonscher.com/res/scrounger.html