I use a theme called 'Opera'. It makes the browser much faster and nicer, and then gives it more features.
*waves his magick wand of expansion to increase the question to Firefox/Opera* Leigh Dark, for all the many Opera users out there who I know are reading this and thinking of ways to subvert it.
i use a really compact theme minifoxflat. i think it's the smallest one out there https://addons.mozilla.org/firefox/1202/ i like my web page viewing space
Click for big: Breeze Simplified, the newer versions I don't like as much but this one is just perfect for my tastes.