Sorry, but Firefox only remembers one previous session. One exception is that Firefox creates a snapshot of your open tabs each time you install an update. Your Firefox reported that it is version 47, so I suspect you don't have any recent update snapshots. If you want to take a look:

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 Directory" button.

In your profile folder, scroll down and double-click into the sessionstore-backups folder. Check the timestamps of the files here, which usually include:

• 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, which I think you already restored
• 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?

Thanks for reply. The first 3 of your "bulleted" files are all timed after I lost the tabs but the last upgrade file is upgrade.js-20160606114208 and is accessed and modified Tue, 27 Sep 2016 16:02:51 which is before I lost the tabs.

Hi kayeselle, to inspect the URLs in that file, you can try this:

(1) Copy that file to your desktop or some more convenient location, for reasons that will be apparent in a moment

(2) Open Firefox's Scratchpad tool using either:

• "3-bar" menu button > Developer > Scratchpad
• (menu bar) Tools > Web Developer > Scratchpad

On the top bar, click Open File, then use the file browser to find the upgrade.js-... file wherever you saved it

Note: On Windows, you need to change from viewing only JavaScript files to viewing all files due to the odd file extension. I don't know whether Linux requires that.

That may take several moments to load if it's a large file.

(3) Then on the top bar of the Scratchpad, click Pretty Print to re-lay-out the file in a more readable way. Assuming that works, you'll see "entries" numerous times, with a list of one or more addresses for that tab. (Example screen shot attached.)

Hopefully you can assess whether your missing tabs are here. You either can copy/paste these URLs to Firefox's address bar to open them, or you could roll up your sleeves and try some alternate methods that are a little more complicated (details if desired).

You don't need to save the "pretty" version unless you find the format helpful for reference.

OK .. looking good, thanks. Seems as if many of them are there. I pasted the contents into LibreOffice Writer so I could get it to "find" 'entries' for me. Even so it's going to take some time to revisit each site manually as there are 13011 lines. I'm happy to take your advice as to the choice between continuing manually or "rolling up my sleeves" if you think an alternative method would be advantageous with this amount of information. Sleep time here now. I'll be able to come back and look either tomorrow or the next day .. which - is unknown till the morning. Thanks again Ken

Hi Ken, I'm going to give you the steps for Windows and hopefully they are similar on Linux.

To try swapping in a session history file from your backup folder so Firefox will load it, the standard "manual swap" method is as follows (assuming Firefox is still running):

(1) From inside Firefox, 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" ("Open Directory"?) button. This should launch a file browser window listing the various files and folders in your profile.

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

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

Pause while Firefox finishes its cleanup -- these changes should occur:

• recovery.js is moved from the sessionstore-backups folder to the main level of the profile folder and renamed to sessionstore.js
• recovery.bak is deleted from sessionstore-backups

(3) Once Firefox has stopped updating things, while viewing the main level of the profile folder, rename sessionstore.js to sessionstore.old

(4) Copy in the other file you want to restore, and rename it to sessionstore.js -- after the rename, Windows should show it right next to sessionstore.old in alphabetical order

(5) Start Firefox and it should read the swapped in sessionstore.js 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?

Thanks Jefferson I'm not going to be able to try till tomorrow night earliest possibly Mon. but will let you know how it goes.

Afraid I've got stuck/lost at :

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

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

Pause while Firefox finishes its cleanup -- these changes should occur:

   recovery.js is moved from the sessionstore-backups folder to the main level of the profile folder and renamed to sessionstore.js
   recovery.bak is deleted from sessionstore-backups 

I exited Firefox, waited (couple of mins) but have three problems 1. recovery.js is still in sessionstore-backups folder 2. I don't know where to look for "main level of the profile folder and renamed to sessionstore.js" 3. recovery.bak is is still in sessionstore-backups

If this might be something that Windows would sort and Ubuntu/Linux wont I could go back to your second response and sift out the info from there.

I don't know why Firefox would work differently on Linux. If necessary, you can rename those two recovery files to hide them from Firefox. The main level of the profile folder is the parent directory of sessionstore-backups -- the one you were looking at in Step #1.

Hi Jefferson Apologies that I faded out on this. I fear my limitations are such that I have struggled to follow what has been happening and what to do despite your careful instructions. I may yet go back and (re)work through your advice above but in the mean time want to know how best to acknowledge in the forum the time and effort you've invested so far. I can't yet click "Solved the problem" but that's my doing not yours. Is there something else I could do ?

If I update to the latest version of UBUNTU will that affect the possibility of retrieving the tabs information ?

Hi kayeselle, as a Windows user, I'm not very familiar with the ins and outs of different Linux distributions. I know that in some cases when you install Firefox from the distribution's package manager it has been pre-customized and may work a bit differently than the basic version Mozilla distributes. But otherwise ??

I think the key thing is to make safe backups of your session history files that you might want to try to restore later, somewhere that an update won't overwrite.