Try the following:

1. Open the about:config page on Firefox
2. Find browser.sessionstore.restore_on_demand
3. Change the value of this string to true

Please report back soon.

Thanks for your help!

So, that option was already set to true. For doubt's sake, I changed it to false, restarted FF, changed it back to true and restated again. Nothing.

Anyway, I did a few more tests and now I'm able to reproduce the few times the restore works: the key seems to be restarting Windows between modified sessions. Below are the steps I did.

1.

• Open a couple of tabs
• Exit FF
• Restart Windows
• Open FF
• Launch "History->Restore"
• IT WORKS

2.

• Exit FF without touching the restored tabs
• Open FF
• Launch "History->Restore"
• IT WORKS (everytime the steps on point 2 are repeated)

3.

• Add/delete a tab in the restored session
• Exit FF
• Open FF
• "History->Restore" is grayed out
• IT DOESN'T WORK

4.

• Repeat steps from point 1 (and optionally from point 2)
• Add/delete a tab in the restored session
• Exit FF
• Restart Windows
• Open FF
• Launch "History->Restore"
• IT WORKS

Also, I don't know if it has anything to do with my problem, but I noticed that, after restarting Windows, FF is kind of slow on the 1st start up.

In case you are using "Clear history when Firefox closes":

• do not clear the Browsing History

• Tools > Options > Privacy > Firefox will: "Use custom settings for history": [X] "Clear history when Firefox closes" > Settings
• https://support.mozilla.org/kb/Clear+Recent+History

Note that clearing "Site Preferences" clears all exceptions for cookies, images, pop-up windows, software installation, and passwords.

You can check the browser.sessionstore.* prefs on the about:config page and reset user set (bold) browser.sessionstore.*prefs to the default value via the right-click context menu to make sure that Session Restore is enabled and working properly.

• http://kb.mozillazine.org/Session_Restore
• https://support.mozilla.org/kb/restore-previous-session

cor-el, I had already tried out your suggestions, they don't work :-(

Does Firefox create a sessionstore.js file in the Firefox profile folder?

Does it work with this startup setting?

• Tools > Options > General > Startup: "When Firefox Starts"
• "Show my windows and tabs from last time"

To cor-el:

Yes, sessionstore.js is present (and sessionstore.bak too).

And yes, selecting the option "Show my windows and tabs from last time" is the only way to recover my tabs during the same Windows session. A few replies above I explained in detail how restarting Windows strangely affects the session restore.

Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) as a test to see if that helps.

Good idea, co-rel!

But nope, sadly useless. Same behaviour from before: no restore during sessions on Safe Mode, and Safe Mode session restored perfectly from "History->Restore" upon returning to Normal Mode.

Any more suggestions, please? This problem is turning out to be quite a struggle!

The sessionstore.bak file is created at every start of Firefox as a copy of the sessionstore.js file saved in the previous session to make it possible to restore the previous session via the History menu at any time during the current session.
So if you can't restore a session at a later time then it sounds that this sessionstore.bak file isn't created.
The about:sessionrestore page should display the content of this file (History > Restore Previous Session).

I have both sessionstore.js and sessionstore.bak, and they both exactly work as you said. I kept an eye on them with notepad, both during navigation and after exiting FF, and the lists of sites I found in them match the penultimate session (sessionstore.bak) and latest session (sessionstore.js).

I tried typing about:sessionrestore in the address bar and I received the message "Oops, this is embarassing" with no tab to restore, although sessionstore.bak listed the sites of the previous session. The strange thing is that, during the same session, while "History->Restore" and "about:sessionrestore" didn't work, the Restore button on the default FF home page (luckily appeared) restored perfectly the previous session just like that...

Did you try to disable all extensions?

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Yes, done that. And already read and followed those instructions. Like I said, uninstalling FF and all the preferences and retrying with a clean install didn't work.

--

There must be something with updating to 23.0.1 that doesn't go well.

I run a few tests on an old PC of mine, where it was still installed a perfectly functional FF 16.0.2. Before connecting to the internet I disabled the automatic updates both in FF-16 and in Comodo Internet Security 5.12 (I wanted to keep an eye on the version of the antivirus, too, in case its recent update was the culprit).

Then I set up two separate sandboxes with Sandboxie: in one of them I updated the old FF to FF 23.0.1, and in the other I updated to FF 24.0b6. Well, the sandbox with FF 23.0.1 manifests the usual problem, while the one with FF 24.0b6 seems to work fine.

To have an additional proof that my customization wasn't the cause of the malfunctioning, I replaced the profile folder of FF-16 with the profile I was using after I updated to FF 23.0.1: as expected, no problems. Obviously some addons were disabled because incompatible with the old version, but this is irrelevant as I already said that FF 23.0.1 doesn't want to work even with default settings and no addons.

I feel pretty disheartened right now...

Good news! The problem seems to have resolved itself with the Firefox 24 update. Finally.

stupid worthless POS browser just started doing the same thing

I had a similar problem to this today.

Firefox crashed, and when I restored the backup session (by replacing the sessionstore.js file) - all that loaded was my homepage.

I created a test profile and my session file would not load in that either, so I guess the session file was just corrupted. When I looked at it in a text editor, it was just all blank data and no English (while the test profile's session file had English).

I really wish Firefox would save more than one backup of the sessionstore because in this case there was absolutely nothing I could have done to save it. It crashed, I re-launched Firefox and my tabs were gone, so I immediately copied the sessionstore files from the profile folder, but all that was left was one new empty file and one corrupt one. Firefox should surely keep 3 or 4 backups? How hard can it be.

I lost too many saved pages and bookmarks because the Restore Previous Sessioin option disappeared from my home page and was grayed out under history. If you're not computer savvy and the complicated suggested fixes are over your head or don't work, save all your Firefox bookmarks to Google Chrome. Delete Firefox and start using Google Chrome. I have never had this problem with Google Chrome.