First: Do not exit Firefox, or if you closed it, don't re-open it.

Let's back up a few files. Here's how:

(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 > "?" 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 "Show Folder" 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, scroll down and double-click into the sessionstore-backups folder. Save all files here to a safe location, such as your Documents folder. If not too much time has passed, we may be able to use them to recover your lost tabs.

(3) What files did you find?

The kinds of files you may find among your sessionstore files are:

• recovery.js: 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.bak: a backup copy of recovery.js
• previous.js: the windows and tabs in your last Firefox session
• upgrade.js-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?

Note: By default, Windows hides the .js extension. To ensure that you are looking at the files I mentioned, you may want to turn off that feature. This article has the steps: http://windows.microsoft.com/en-us/windows/show-hide-file-name-extensions

Thank you so much for the detailed reply. first I need to tell you that unfortunately I closed Firefox more than once since I lost the tabs. I am a humble comp user so it took me some time to follow those steps and yes I did find the files you mentioned. I will copy the names of the files I found on the profile folder:

1- previous 2- recovery.bak 3- recovery 4- upgrade.js-20170316213829 5- upgrade.js-20170323105023 6- upgrade.js-20170413192749

I am hoping that this will be enough to recover the tabs.

Thanks again for your time and effort

If you set Windows Explorer to the Details view with columns showing the date and time, are there any files newer than the one called "upgrade.js-20170413192749" but not so new that they are too recent to be useful?

I have to run, so let me link you to an old post about how you can check the contents of and use those files: https://support.mozilla.org/questions/1151794#answer-947125