Backup Firefox History & Extensions
It is important to keep the extensions and their settings whenever reinstalling windows or use the same profile on notebook or any other PC.
Easy Method
Download Mozback and take the backup
Manual Method
In Windows XP
In the folder Documents and Settings for current user in C or any other drive the OS is installed you will find Application Data\Mozilla. Copy and keep the Mozilla folder anywhere in safe place, whenever you need the backup to be restored just copy and replace the Firefox folder there.
Also, copy and backup the contents from C:\Documents and Settings\USER\Local Settings\Application Data\Mozilla, this contains cache and history of firefox.
Note: Application Data & Local Settings are Hidden Folder, so you should need to Enable View Hidden Folder from Folder Options.