Sounds like a severe mixup somewhere. In case the installer didn't fully clean out the old program files, you can replace them without disturbing your settings using this Clean Reinstall procedure:

(1) Download a fresh installer for Firefox 33 from https://www.mozilla.org/firefox/all/ to a convenient location. (Scroll down to your preferred language.)

(2) If applicable, exit out of Firefox or make sure it is fully terminated in Task Manager.

(3) Rename the program folder

(32-bit Windows folder names)

C:\Program Files\Mozilla Firefox

to

C:\Program Files\OldFirefox

(64-bit Windows folder names)

C:\Program Files (x86)\Mozilla Firefox

to

C:\Program Files (x86)\OldFirefox

(4) Run the installer you downloaded in #1. It should automatically connect to your existing settings.

You might need to exit and start again to test whether Firefox is now remembering preference changes.

Note: Some recently installed plugins may exist only in that OldFirefox folder. If something essential is missing, look in these folders:

• \OldFirefox\Plugins
• \OldFirefox\browser\plugins

Will Firefox start?

What security software (firewall, anti-virus) do you have?

Thanks for your quick reply,but that did not work and still getting the same error. I'm using Sandboxie,no other antivirus or firewall software.

I'm not familiar with how Sandboxie works. Does it use your actual Firefox settings folder or a separate copy that it manages? What happens if you try to start Firefox normally?