I notice you use the Session Manager extension, so what I'm going to suggest might be a bit different on your system, but let's try it anyway:

The standard "manual swap" method is as follows (assuming Firefox is still running):

(1) 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. This should launch a new window listing various files and folders in Windows Explorer.

(2) Scroll down and double-click into the sessionstore-backups folder. Save all files here to a safe location, such as your Documents folder. You probably won't need all of them, but...

(3) 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

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

(5) Copy in the file you want to restore -- in this case, the latest file named similarly to upgrade.js-build_id -- and rename it to sessionstore.js -- Windows should show it right next to sessionstore.old in alphabetical order

Note: the file name must be exact. By default, Windows hides the .js file extension. For best results in renaming files, I recommend showing all file extensions. See: http://windows.microsoft.com/en-us/windows/show-hide-file-name-extensions

(6) Start Firefox and it should read 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?

There are other things that need attention.

The System Details List shows that you have multiple Flash plugins.

1. Shockwave Flash 19.0 r0
2. Shockwave Flash 21.0 r0

You can find the installation path of all plugins on the about:plugins page.

• http://kb.mozillazine.org/Issues_related_to_plugins#Identifying_installed_plugins

You can check the Flash player installation folder for multiple Flash player plugins and remove older version(s) of the plugin (NPSWF32) and possibly (re)install the latest Flash player.

• (32 bit Windows) C:\Windows\System32\Macromed\Flash\
• (64 bit Windows) C:\Windows\SysWOW64\Macromed\Flash\

So I tried the previous fix by jscher2000. It didn't go exactly as all that, but I think I worked around it by cutting and pasting. It didn't seem to fix the problem, but then I tried loading an old session and then a newer one from Session Manager and that seems to have fixed it.