This is installable through an add-on which enables the user to change the visual aspects of the web browser without downloading and installing themes.
Persona selector in this add-on loads dynamically and they are supplying a couple of usable enhancements.
Features of Personas for Firefox:
You can select a Persona from the dynamic menus and see results instantly without having to discover, select, download or install a separate bit of software or code.
Personas can be added, removed or updated by their designers at any time, without requiring a software update.