This unnecessary folder holds your bookmarks, passwords, history, sessions and more.

Are you having any issues with the new Profile that was created ?

If not needing them then shut Firefox down from 3Bar Menu --> Exit . Then delete the file. You may have to boot into Safe Mode to delete the file if above does not work. Please let us know if this solved your issue or if need further assistance.

No it didn't help. I remove the installation file. But for somehow the 'Old Firefox Data' is not removing. It said I have to have an administrator's permission to delete it and I am the administrator of my account. Any other solution?

Usually that is a error that can be fixed by shutting down and restarting as Windows still sees it as having elevated permissions which will be dropped if Reboot.

Right Click Properties and change permissions.

Did you boot Windows to safe mode and try to delete it ?

http://smallbusiness.chron.com/force-delete-windows-command-line-54175.html

Thanks a lot Pkshadow. It worked!!!!!

)