Ever since I started using Firefox, my favorite has always been the Mac OS style Brushed theme created by Elvo. It is elegant, easy on the eyes and leaves maximum amount of space for the content on websites. Says its not compatible with the latest version of Firefox but I just disable the add-on compatibility check and it works perfectly fine with mine (version 126.96.36.199). What's more, you can easily customize it with different focus glows, rounded or rectangular input boxes, and regular or inversed tabs.
If the theme doesn't work no matter what you do then Huji made a version compatible with Firefox 2. It works, but as you can see from his screenshot the tabs still need a bit more improvement to match up the original design.
I have also customized the startup (boot) screen on my Windows XP laptop using the BootSkin software and the Brushed bootskin by Jyrik.
To match my Windows Explorer's look with the rest, I used the Toolbar Wallpaper software and made a Brushed tile image. It also changes the background of the Internet Explorer 6 that is installed, but then again I hardly use it to surf the net.
I didn't forget my favorite music player Winamp either! Here is the Brushed skin for it.
Now my computer looks fully dressed! Before you go off to download all these goodies, I have a couple of questions for you.
1. What is your favorite look and feel?
2. Which themes/skins are you using?