Follow These Steps :
1) Install talk and comment Extension From Here.
2) Once installed , click on Allow.
3)Now log in to Facebook and authorize the application of Talk and Comment.
4) Finally refresh Facebook home page. then you can see Mic sign beside comment and in message box.
5) Click and hold mic icon until it turns Red.
6) Record you Message and release Mic icon to upload the message.
7) Once uploaded, you will receive a link for you voice comment.
8) Just hit Enter to post it.
9) Now your friend can see play button if they are using using Talk and Comment Extension.
Note : Everyone (according to your privacy setting) can hear your comment. if they have Talk and Comment installed then they will see a playable button else, they will see a link to your comment opening in new window will a play button.
Others can see comment with Talk And Comment link.
Hope you have liked this new trick of Facebook. Enjoy using voice comments in Facebook.