In case you use "Clear history when Firefox closes".

• do not clear the Browsing History

• Options/Preferences -> Privacy & Security -> Firefox will: "Use custom settings for history": [X] "Clear history when Firefox closes" -> Settings
• https://support.mozilla.org/en-US/kb/delete-browsing-search-download-history-firefox

• clearing "Site Preferences" clears exceptions for cookies, images, pop-up windows, and software installation and exception for password and other website specific data
• clearing "Cookies" will remove all selected cookies including cookies with an "Allow" exception you may want to keep

Hi there, these are my settings:

History: FF [use custom settings ] [ ] Private browsing [ ] Preserve browsing history + downloads---I ticked this one but the same [ ] Preserve search history + forms [ν] Accept cookies from webpages Accept cookies from[visited] Keep until [FF closes] [ν] Clear history when FF closes

PrtScn

What is checked if you open the settings?

• "Clear history when Firefox closes" -> Settings (Ρυθμίσεις)

Could you back up your existing session history files? Here's how:

You can open your current Firefox settings (AKA Firefox profile) folder using either

• "3-bar" menu button > "?" button > 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.

In your profile folder, double-click into the sessionstore-backups folder. Save all files here to a safe location.

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

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? The last upgrade file might be the best candidate, but in order to see what's in there, you can drag and drop the file onto this page, then click Scrounge URLs: https://www.jeffersonscher.com/res/scrounger.html

(That tool is on my site, so please let me know if it doesn't work for you.)

This is a crude URL-mining tool that does not distinguish between pinned tabs and regular tabs, but maybe it will be useful in some way.

PrtScn

At this point I have to say that thisafter the update I made a format also. I tried then to setup a fresh copy but I couldn't find the very latest version in GR so I installed the english.

Then I removed the english and installed the latest GR.

I don't know if this matters on term of tryin' to detect "when" this happened with sessionstore files..

In the lower part of this screenshot, it seems that you have Firefox set to delete browsing history at shutdown:

https://prod-cdn.sumo.mozilla.net/uploads/images/2018-01-18-03-54-52-cfcd20.png

That will delete your tabs, too.

Like I wrote in my first reply:

In case you use "Clear history when Firefox closes".

• do not clear the Browsing History

You need to remove the checkmark on "Browsing and Download History". Tabs are considered as history and clearing history that way prevails and prevent Firefox from reopening tabs on the next start.

Thank you very much both of you guys!

With the current setting works fine....!

Just to confuse things . . . or perhaps help someone else in the same boat: Here's what happened to me I couldn't get the "pin tabs" option to show up, so I was searching among my settings and finally went to "My Account," where I clicked on "Devices" and discovered that somehow the name for the current device was incorrect (I have two devices with Firefox on both, and the name that appeared was the name of the other device). Apparently my computer knew that, but Firefox didn't . . . or vice versa, but neither of them knew enough to tell me there was a problem! Anyhow, I disconnected that account, signed in again, and this time the right device name showed up, as did the "Pin Tab" option. BINGO!