In my work with Brand Thunder, one of the things we've struggled with is bundling an extension and theme together as one package. To accomplish this, we had created an extension that installs a theme at startup. This worked, but created some confusion when trying to uninstall. We finally have a solution to this - it's called the Brand Thunder Boom!
Brand Thunder Booms are like Personas on steroids. Booms don't just change a background image; they provide lightweight theming that can change background images, colors, navigation buttons and even tabs. They can also add toolbars with custom navigation and widgets for a particular brand as well as sidebars for things like videos or news feeds.
Booms also support dynamic switching. So if you have five booms installed, you can move between them without restarting your browser.