Voice of my experience

I generally take a backup of the extensions and bookmark of my Firefox to synchronize the setting between my home computer and the computer at my work place.

You will need to install an extension FEBE(Firefox Environment Backup Extension). This extension after installation will create a menu under tools and provides you with lot of backup options, in those options you have extension backup and bookmark backup.

Here is a link where you can download the latest version of FEBE

There is another extension CLEO(Compact Library Extension Organizer) that can be used to combine all the extension and make it as a single extension file. it can also be very help full if you have your own custom made extension.

Here is a link where you can download the latest version of CLEO