Firefox personas is a way to personalize your firefox browser. It also makes your browser look more visually appealing versus just the plain default gray. There are many "skins" available to choose from. There is a search bar in the top right of the main screen to find specific designs you like. There is also many categories to choose from if you don't know something to specifically search. Your firefox needs to be updated with the correct software, but on the main screen of the website they provide a link to download it if you don't already have it.
Click this link to go to the website: http://www.getpersonas.com