Facebook have bunch of smileys that convert the text like :) , :P , :(, 3:) to yellow smileys. You can use these smileys by using codes like in chatbox , status, and comment box . Since these smileys are not visible most of user mightn’t have noticed it. You can make them visible in chatbar using the Firefox addon called “Facebook ChatBar” it can be downloaded from here .
Here are the complete list of facebook smiley codes.
Also check : Facebook comment smiley