One of the things that the Opera browser does way better than Firefox is skinning. In Opera you can go to their skin site, find a theme that you want to install, and preview it immediately in the browser. No restart is required.
Mozilla looks as though they are experimenting with a similar method via an extension called Personas. With Personas you’ll be able to perform basic skinning operations in Firefox without ever needing to restart the browser.
All of the goodness happens in the bottom-left corner of the Status Bar. That’s where a little icon will appear once you’ve installed the extension, and clicking on that icon will immediately present a list of themes that can be chosen. They’re organized according to the most popular, newest ones, and also broken up into categories. As of right now there are a few dozen different themes available for Personas users.
It’s important to note that these themes are not the same as the ones you download from Mozilla’s add-on site. The Personas themes do not skin any of the buttons or the Control Panel area, and the only changes you’ll really see is a new background image behind the Menus, Address Bar, Bookmarks, Tabs, and Status Bar. Despite being such a basic skinning alternative I did find that the themes give Firefox a refreshing appearance.
Now one can only hope that this will result in full skinning capabilities down the road, and that they’ll apply a similar technology to extension installation. Maybe Mozilla will be able to make restarting the browser a thing of the past!