For a long time i was wondering, how to save firefox settings,bookmarks,themes and extensions as always there are chances of windows reluctant to boot up,hard disk failure etc etc. and all of your firefox hard work can be gone in a flash.A lot of my friends recommended me different applications but i myself figured out a way and i think it is the most easiest way of doing the backup.
First, go to C:\Documents and Settings\yourusername\ApplicationData\Mozilla\Firefox.There you will find

Firefox profiles 1

i)A profiles folder and
ii)a profiles.ini(a notepad file).

i)Inside the profiles folder you will find a folder like this.

Firefox profiles 2

In mine case it is cvkgefzk.default.This folder contains all your Firefox Settings,bookmarks,themes and extensions.Backup this folder on any of your other hard drives.
ii)Open up your profiles.ini file.It contains the path to my default profiles folder such as cvkgefzk.default.

Firefox profiles 3

So whenever you want to restore your Firefox settings,bookmarks,themes and extensions,then first you have to paste your profile folder and secondly you have to
change the name in your profiles.ini file.

And now your firefox is restored in a flash! As shiny as before.