I’ve seen numerous pages on facebook about changing facebook themes. Unfortunately, no user can change his/her profile theme because this data has to be stored on server. It can only happen if facebook starts supporting themes which I don’t see is a possibility anytime in near future.
Before following this tutorial, keep 1 things in mind:
This change will only be seen by you only on your computer and only on Mozilla Firefox.
This means that its only for people who would like to feel good seeing their own themes. It would not affect the look of your profile on others’ computer ie. other people would not be able to see your theme and instead see the default facebook theme.