Personas for Firefox does essentially what Hotbar did for IE, except it doesn’t pollute your PC with all sorts of nefarious software. This comparison isn’t quite fair though. Personas has drawn on the experiences of Web 2.0 to provide a simpler immersive themed atmosphere.
A Persona is an extremely simple way to theme your browser. There are five parts that make up a Firefox Persona. The header image is shown behind the menu bar, the navigation toolbar, the bookmarks toolbar and any other toolbars you have up the top. You set it as a 3000x200pixel image. The footer (a 3000x100px image) is shown behind the status bar and if show the search bar. You also set a text colour and an accent colour for any text that will be shown in front of your backgrounds. Finally you set a name for your theme as you upload it to Mozilla.
The best thing Personas has over themes is that you don’t have to restart Firefox in order to apply them. This leads to some especially neat features, for example while browsing for a new persona for your browser when you mouse over a persona it gets applied as a preview. This means effectively when you are looking for themes you get to see exactly what they’ll looks like before you pick them. You can get Personas from Mozilla labs, or at its dedicated website. Also see Mozilla’s blog post about Personas.
Random Thought: The Linux kernel must have a bad heart, every time it panics it dies.