I love Firefox. Addons (extensions and themes) are the icing on the foxy cake. However, installation always requires a restart. Firefox needs to take a leaf out of Opera's book and install and run without a restart.

However, weep no more with envy at Opera. You can now add and run themes dynamically in Firefox with the Persona extensions. Once installed you can change themes on the fly. These themes are accessed online from Mozilla Labs. Easy and lots of fun. Follow the link above and try them out