What do the -moz-*, -ms-*, -webkit-*, -o-* and -khtml-* properties do?

This are the format for vendor specific browser. most of browser implemented extension adding new features for testing & debuggin purpose before they available for new CSS specification.

For using this vendor specific extension CSS specification define a specific format that vendor should follow the format that is 

'- ' or '_' + vendor specific identifier + '-' + meaningful name

as format indicate the keyword & property name start with dash or underscore  this allow the vendor specific css property  not conflict with regular css property as according to  css specification css property never start with "dash" or "underscore"

Many css property in css specification required vendor specification to implement in particular browser for example opacity property that few browser not support without using vendor specific properties

Vender-test

{

  -moz-opacity:0.6;         /* Mozilla extension */

  -khtml-opacity:0.6;        /* Konqueror extension (Safari1.1)*/

  opacity:0.6;          

}