A working draft means experimental
Monday, January 16, 2012 1:34:08 PM
Browser Support The font-feature-settings property is currently supported by Firefox 4+ and Internet Explorer 10, beginning with Preview 4. Note that because Firefox and IE implemented different versions of the draft the value syntax they accept is different. For example, enabling kerning in both browsers requires the following:-ms-font-feature-settings: "kern" 1; -moz-font-feature-setting: "kern=1";
Testing and playing with them. That's very good too. Deploying them in production sites. Not yet. Flexbox is a recent example of the issues it creates when you run for interoperability and inclusive market shares.