You may have corrupt sessionstore file(s).

Type about:support in the address bar and press enter.

Under the page logo on the left side you will see Application Basics. Under this find Profile Folder. To it’s right press the button Show Folder. This will open your file browser to the current Firefox profile. Now Close Firefox.

Locate the sessionstore file(s). Then rename or delete them. Restart Firefox.

Hi FredMcD,

Thanks for the reply, but as I said, I did try session restores, which included this. (I realise I wasn't very clear about that though, so I apologise.) It did nothing for me, as the only files there seemed to relate to the then-current session (which had a bunch of Mozilla support tabs) or the one before it, which had been opened immediately after the restart (and did not have the support tabs, but all the empty tabs).

There is a file called "upgrade.js-20151221130713" and if I can use that I'm more than happy to, as it's from a few days ago, but I fear it's more to do with the recent, and multiple, updates Firefox has been doing.

Thanks again for your help, and if you have any further suggestions, I'd be happy to hear them.  :)

If you consider your tabs important then best is to bookmark them via the star on the Navigation Toolbar. If you get a script warning when Firefox is starting up then best is to click continue to see if the script finishes properly instead of stopping the script.

Do you have extensions installed that might be causing this script error?

Start Firefox in Safe Mode to check if one of the extensions (Firefox menu button/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem.

• Switch to the DEFAULT theme: Firefox menu button/Tools > Add-ons > Appearance
• Do NOT click the Reset button on the Safe Mode start window

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

Your only option to get back at least some of the tabs might be via the upgrade.js file that Firefox creates automatically when you update Firefox.

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

previous.js (cleanBackup: copy of sessionstore.js from previous session that was loaded successfully)
recovery.js (latest version of the sessionstore written during runtime)
recovery.bak (previous version of the sessionstore written during runtime)
upgrade.js-<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.js to replace the current file (make a backup copy of the current sessionstore.js).

See also:

• http://www.ghacks.net/2014/06/27/mozilla-launches-improved-session-restore-firefox-33/

Hi cor-el,

Thanks for the reply. I am aware of the bookmark function, and use it regularly.

I only have the default extensions installed, and none of them seem to have cause the script error, according to Safe Mode. That was also not my issue, I just wanted to give background to how the situation occured.

As I said to FredMcD above, I have an upgrade.js file from a few days ago I would be happy to use. However, when I copy the file and change its name, the file type changes to simply "File".

If someone could tell me how to use it without it changing, I'd appreciate it.

Thanks again for your help, and if you have any further suggestions, I'd be happy to hear them.  :)

I think you removed the extension of the file. In other words, without the extension, the computer does not know what to do with it.

Try to add quotes around the name when you rename the file ("sessionstore.js") and make sure that Windows isn't hiding the .js file extension.

Hi FredMcD,

How on earth could I have managed to do that? O.o