Personas is an extension or is it a theme? Both actually, it is extension that “adds lightweight theming” to your Firefox. Lightweight in that it only does the main browser window, not any of the options, bookmarks, downloads, etc. windows. There are several Personas to choose from and they apply on-the-fly (no restart needed once the extensions is installed). Personas is a prototype that builds upon the ideas that:

• themes today are too hard to find, install and use
• graphic designers should be able to style the browser without having to code
• browsers can be more than just desktop software, they can include online components
• people just want their computer to be a little more fun and personal

A couple troubleshooting tips I can offer. This works best if you use the Default Firefox theme and if the menu bar becomes de-skinned, this will be fixed the next time you restart.

Update 06/15/2011 – Personas Plus is the next generation of Personas and works with Firefox 3.6 and newer.